Merge pull request #487 from 3b1b/ode

Ode

active_projects/ode/all_part1_scenes.py

@@ -6,8 +6,11 @@ from active_projects.ode.part1.wordy_scenes import *
 
 OUTPUT_DIRECTORY = "ode/part1"
 ALL_SCENE_CLASSES = [
+    WhenChangeIsEasier,
+    VectorFieldTest,
     IntroducePendulum,
     MultiplePendulumsOverlayed,
+    PeriodFormula,
     FormulasAreLies,
     MediumAnglePendulum,
     MediumHighAnglePendulum,
@@ -18,21 +21,57 @@ ALL_SCENE_CLASSES = [
     VeryLowAnglePendulum,
     FormulasAreLies,
     TourOfDifferentialEquations,
+    WherePendulumLeads,
+    LongDoublePendulum,
     # FollowThisThread,
     StrogatzQuote,
+    ShowHorizontalDashedLine,
+    RabbitFoxPopulations,
+    RabbitFoxEquation,
     # Something...
+    ShowSimpleTrajectory,
+    SimpleProjectileEquation,
+    SimpleProjectileEquationVGraphFreedom,
     ShowGravityAcceleration,
+    UniversalGravityLawSymbols,
+    ExampleTypicalODE,
     AnalyzePendulumForce,
+    ShowSineValues,
     BuildUpEquation,
+    AirResistanceBrace,
     ShowDerivativeVideo,
     SubtleAirCurrents,
+    SimpleDampenedPendulum,
     DefineODE,
+    SecondOrderEquationExample,
     ODEvsPDEinFrames,
     ProveTeacherWrong,
     SetAsideSeekingSolution,
-    ReferencePiCollisionStateSpaces,
+    #
+    WriteInRadians,
+    XEqLThetaToCorner,
+    ComingUp,
+    InputLabel,
+    SoWhatIsThetaThen,
+    ReallyHardToSolve,
+    ReasonForSolution,
+    PhysicistPhaseSpace,
+    GleickQuote,
+    SpectrumOfStartingStates,
+    WritePhaseFlow,
+    AskAboutStability,
+    LoveExample,
+    PassageOfTime,
+    LovePhaseSpace,
+    ComparePhysicsToLove,
+    FramesComparingPhysicsToLove,
+    SetupToTakingManyTinySteps,
+    ShowClutterPrevention,
+    # VisualizeHeightSlopeCurvature,
     VisualizeStates,
+    ReferencePiCollisionStateSpaces,
     IntroduceVectorField,
+    XComponentArrows,
     BreakingSecondOrderIntoTwoFirstOrder,
     ShowPendulumPhaseFlow,
     ShowHighVelocityCase,
@@ -42,10 +81,27 @@ ALL_SCENE_CLASSES = [
     LorenzVectorField,
     ThreeBodiesInSpace,
     AltThreeBodiesInSpace,
+    TwoBodiesInSpace,
+    TwoBodiesWithZPart,
+    ThreeBodyTitle,
     ThreeBodySymbols,
+    #
+    HighAmplitudePendulum,
+    WritePhaseSpace,
+    #
     AskAboutActuallySolving,
     WriteODESolvingCode,
     TakeManyTinySteps,
+    ManyStepsFromDifferentStartingPoints,
     InaccurateComputation,
     HungerForExactness,
+    ShowRect,
+    ShowSquare,
+    JumpToThisPoint,
+    ThreeBodyEquation,
+    ItGetsWorse,
+    ChaosTitle,
+    RevisitQuote,
+    EndScreen,
+    Thumbnail,
 ]

active_projects/ode/all_part2_scenes.py

@@ -0,0 +1,19 @@
+from active_projects.ode.part2.staging import *
+from active_projects.ode.part2.fourier_series import *
+from active_projects.ode.part2.heat_equation import *
+
+OUTPUT_DIRECTORY = "ode/part2"
+ALL_SCENE_CLASSES = [
+    # Tests
+    FourierOfPiSymbol,
+    FourierOfPiSymbol5,
+    FourierOfTrebleClef,
+    # CirclesDrawingWave,
+    # Scenes for video
+    ExplainCircleAnimations,
+    FourierSeriesIntro,
+    FourierSeriesIntroBackground4,
+    FourierSeriesIntroBackground8,
+    FourierSeriesIntroBackground12,
+    FourierSeriesIntroBackground20,
+]

active_projects/ode/part1/pendulum.py

@@ -287,6 +287,9 @@ class ThetaVsTAxes(Axes):
         y_axis.label = theta_label
         y_axis.add(theta_label)
 
+        self.y_axis_label = theta_label
+        self.x_axis_label = t_label
+
         x_axis.add_numbers()
         y_axis.add(self.get_y_axis_coordinates(y_axis))
 
@@ -357,6 +360,7 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
             "length": 3,
             "top_point": 4 * RIGHT,
             "weight_diameter": 0.35,
+            "gravity": 20,
         },
         "theta_vs_t_axes_config": {
             "y_max": PI / 4,
@@ -366,6 +370,7 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
                 "unit_size": 2,
                 "tip_length": 0.3,
             },
+            "x_max": 12,
             "number_line_config": {
                 "stroke_width": 2,
             }
@@ -378,12 +383,13 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
 
     def construct(self):
         self.add_pendulum()
-        self.label_pi_creatures()
+        # self.label_pi_creatures()
         self.label_pendulum()
         self.add_graph()
+        self.label_function()
         self.show_graph_period()
         self.show_length_and_gravity()
-        self.tweak_length_and_gravity()
+        # self.tweak_length_and_gravity()
 
     def create_pi_creatures(self):
         randy = Randolph(color=BLUE_C)
@@ -437,7 +443,7 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
             GrowArrow(morty_label.arrow),
             morty.change, "raise_right_hand",
         )
-        self.wait()
+        self.wait(2)
 
     def label_pendulum(self):
         pendulum = self.pendulum
@@ -446,18 +452,18 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
         rect = SurroundingRectangle(label, buff=0.5 * SMALL_BUFF)
         rect.add_updater(lambda r: r.move_to(label))
 
-        self.add(rect)
+        for pi in randy, morty:
+            pi.add_updater(
+                lambda m: m.look_at(pendulum.weight)
+            )
+
+        self.play(randy.change, "pondering")
+        self.play(morty.change, "pondering")
+        self.wait(3)
+        randy.clear_updaters()
+        morty.clear_updaters()
         self.play(
             ShowCreationThenFadeOut(rect),
-            ShowCreationThenDestruction(
-                label.copy().set_style(
-                    fill_opacity=0,
-                    stroke_color=PINK,
-                    stroke_width=2,
-                )
-            ),
-            randy.change, "pondering",
-            morty.change, "pondering",
         )
         self.wait()
 
@@ -467,7 +473,10 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
         axes.to_corner(UL)
 
         self.play(
-            Restore(self.camera_frame),
+            Restore(
+                self.camera_frame,
+                rate_func=squish_rate_func(smooth, 0, 0.9),
+            ),
             DrawBorderThenFill(
                 axes,
                 rate_func=squish_rate_func(smooth, 0.5, 1),
@@ -481,10 +490,30 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
             ),
             run_time=3,
         )
-        self.wait(2)
-        self.graph = axes.get_live_drawn_graph(self.pendulum)
 
+        self.wait(1.5)
+        self.graph = axes.get_live_drawn_graph(self.pendulum)
         self.add(self.graph)
+
+    def label_function(self):
+        hm_word = TextMobject("Simple harmonic motion")
+        hm_word.scale(1.25)
+        hm_word.to_edge(UP)
+
+        formula = TexMobject(
+            "=\\theta_0 \\cos(\\sqrt{g / L} t)"
+        )
+        formula.next_to(
+            self.axes.y_axis_label, RIGHT, SMALL_BUFF
+        )
+        formula.set_stroke(width=0, background=True)
+
+        self.play(FadeInFrom(hm_word, DOWN))
+        self.wait()
+        self.play(
+            Write(formula),
+            hm_word.to_corner, UR
+        )
         self.wait(4)
 
     def show_graph_period(self):
@@ -503,13 +532,7 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
         line.shift(SMALL_BUFF * RIGHT)
         brace = Brace(line, UP, buff=SMALL_BUFF)
         brace.add_to_back(brace.copy().set_style(BLACK, 10))
-        formula = TexMobject(
-            "\\sqrt{\\,", "2\\pi", "L", "/", "g", "}",
-            tex_to_color_map={
-                "L": BLUE,
-                "g": YELLOW,
-            }
-        )
+        formula = get_period_formula()
         formula.next_to(brace, UP, SMALL_BUFF)
 
         self.period_formula = formula
@@ -537,29 +560,22 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
             self.pendulum,
             length_multiple=0.5 / 9.8,
         )
+        down_vectors = self.get_down_vectors()
+        down_vectors.set_color(YELLOW)
+        down_vectors.set_opacity(0.5)
 
-        self.play(ShowCreationThenDestructionAround(L))
-        dot = Dot(fill_opacity=0.25)
-        dot.move_to(L)
         self.play(
+            ShowCreationThenDestructionAround(L),
             ShowCreation(new_rod),
-            dot.move_to, new_rod,
-            dot.fade, 1,
         )
-        self.remove(dot)
         self.play(FadeOut(new_rod))
-        self.wait()
 
-        self.play(ShowCreationThenDestructionAround(g))
-        dot.move_to(g)
-        dot.set_fill(opacity=0.5)
         self.play(
+            ShowCreationThenDestructionAround(g),
             GrowArrow(g_vect),
-            dot.move_to, g_vect,
-            dot.fade, 1,
         )
-        self.remove(dot)
-        self.wait(2)
+        self.play(self.get_down_vectors_animation(down_vectors))
+        self.wait(6)
 
         self.gravity_vector = g_vect
 
@@ -593,15 +609,7 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
         # new_pendulum_config["initial_theta"] = pendulum.get_theta()
         new_pendulum = Pendulum(**new_pendulum_config)
 
-        down_vectors = VGroup(*[
-            Vector(0.5 * DOWN)
-            for x in range(10 * 150)
-        ])
-        down_vectors.arrange_in_grid(10, 150, buff=MED_SMALL_BUFF)
-        down_vectors.set_color_by_gradient(BLUE, RED)
-        # for vect in down_vectors:
-        #     vect.shift(0.1 * np.random.random(3))
-        down_vectors.to_edge(RIGHT)
+        down_vectors = self.get_down_vectors()
 
         self.play(randy.change, "happy")
         self.play(
@@ -624,10 +632,7 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
         g_vect.scale(2)
         self.play(
             FadeOut(graph2),
-            LaggedStart(*[
-                GrowArrow(v, rate_func=there_and_back)
-                for v in down_vectors
-            ], lag_ratio=0.0005, run_time=2, remover=True)
+            self.get_down_vectors_animation(down_vectors)
         )
         self.play(
             FadeIn(graph3),
@@ -635,6 +640,30 @@ class IntroducePendulum(PiCreatureScene, MovingCameraScene):
         )
         self.wait(6)
 
+    #
+    def get_down_vectors(self):
+        down_vectors = VGroup(*[
+            Vector(0.5 * DOWN)
+            for x in range(10 * 150)
+        ])
+        down_vectors.arrange_in_grid(10, 150, buff=MED_SMALL_BUFF)
+        down_vectors.set_color_by_gradient(BLUE, RED)
+        # for vect in down_vectors:
+        #     vect.shift(0.1 * np.random.random(3))
+        down_vectors.to_edge(RIGHT)
+        return down_vectors
+
+    def get_down_vectors_animation(self, down_vectors):
+        return LaggedStart(
+            *[
+                GrowArrow(v, rate_func=there_and_back)
+                for v in down_vectors
+            ],
+            lag_ratio=0.0005,
+            run_time=2,
+            remover=True
+        )
+
 
 class MultiplePendulumsOverlayed(Scene):
     CONFIG = {
@@ -868,6 +897,95 @@ class VeryLowAnglePendulum(LowAnglePendulum):
     }
 
 
+class WherePendulumLeads(PiCreatureScene):
+    def construct(self):
+        pendulum = Pendulum(
+            top_point=UP,
+            length=3,
+            gravity=20,
+        )
+        pendulum.start_swinging()
+
+        l_title = TextMobject("Linearization")
+        l_title.scale(1.5)
+        l_title.to_corner(UL)
+        c_title = TextMobject("Chaos")
+        c_title.scale(1.5)
+        c_title.move_to(l_title)
+        c_title.move_to(
+            c_title.get_center() * np.array([-1, 1, 1])
+        )
+
+        get_theta = pendulum.get_theta
+        spring = always_redraw(
+            lambda: ParametricFunction(
+                lambda t: np.array([
+                    np.cos(TAU * t) + (1.4 + get_theta()) * t,
+                    np.sin(TAU * t) - 0.5,
+                    0,
+                ]),
+                t_min=-0.5,
+                t_max=7,
+                color=GREY,
+                sheen_factor=1,
+                sheen_direction=UL,
+            ).scale(0.2).to_edge(LEFT, buff=0)
+        )
+        spring_rect = SurroundingRectangle(
+            spring, buff=MED_LARGE_BUFF,
+            stroke_width=0,
+            fill_color=BLACK,
+            fill_opacity=0,
+        )
+
+        weight = Dot(radius=0.25)
+        weight.add_updater(lambda m: m.move_to(
+            spring.points[-1]
+        ))
+        weight.set_color(BLUE)
+        weight.set_sheen(1, UL)
+        spring_system = VGroup(spring, weight)
+
+        linear_formula = TexMobject(
+            "\\frac{d \\vec{\\textbf{x}}}{dt}="
+            "A\\vec{\\textbf{x}}"
+        )
+        linear_formula.next_to(spring, UP, LARGE_BUFF)
+        linear_formula.match_x(l_title)
+
+        randy = self.pi_creature
+        randy.set_height(2)
+        randy.center()
+        randy.to_edge(DOWN)
+        randy.shift(3 * LEFT)
+        q_marks = TexMobject("???")
+        q_marks.next_to(randy, UP)
+
+        self.add(pendulum, randy)
+        self.play(
+            randy.change, "pondering", pendulum,
+            FadeInFromDown(q_marks, lag_ratio=0.3)
+        )
+        self.play(randy.look_at, pendulum)
+        self.wait(5)
+        self.play(
+            Animation(VectorizedPoint(pendulum.get_top())),
+            FadeOutAndShift(q_marks, UP, lag_ratio=0.3),
+        )
+        self.add(spring_system)
+        self.play(
+            FadeOut(spring_rect),
+            FadeInFrom(linear_formula, UP),
+            FadeInFromDown(l_title),
+        )
+        self.play(FadeInFromDown(c_title))
+        self.wait(8)
+
+
+class LongDoublePendulum(ExternallyAnimatedScene):
+    pass
+
+
 class AnalyzePendulumForce(MovingCameraScene):
     CONFIG = {
         "pendulum_config": {
@@ -885,19 +1003,20 @@ class AnalyzePendulumForce(MovingCameraScene):
 
     def construct(self):
         self.add_pendulum()
+        self.show_arc_length()
         self.add_g_vect()
         self.show_constraint()
         self.break_g_vect_into_components()
-        self.show_gsin_formula()
-        self.show_acceleration_at_different_angles()
         self.show_angle_geometry()
-        self.ask_about_what_to_do()
+        self.show_gsin_formula()
+        self.show_sign()
+        self.show_acceleration_formula()
+        # self.ask_about_what_to_do()
 
-        self.emphasize_theta()
-        self.show_arc_length()
-        self.show_angular_velocity()
-        self.show_angular_acceleration()
-        self.circle_g_sin_formula()
+        # self.emphasize_theta()
+        # self.show_angular_velocity()
+        # self.show_angular_acceleration()
+        # self.circle_g_sin_formula()
 
     def add_pendulum(self):
         pendulum = Pendulum(**self.pendulum_config)
@@ -910,6 +1029,97 @@ class AnalyzePendulumForce(MovingCameraScene):
         self.pendulum = pendulum
         self.theta_tracker = theta_tracker
 
+    def show_arc_length(self):
+        pendulum = self.pendulum
+        angle = pendulum.get_theta()
+        height = pendulum.length
+        top = pendulum.get_fixed_point()
+
+        line = Line(UP, DOWN)
+        line.set_height(height)
+        line.move_to(top, UP)
+        arc = always_redraw(lambda: Arc(
+            start_angle=-90 * DEGREES,
+            angle=pendulum.get_theta(),
+            arc_center=pendulum.get_fixed_point(),
+            radius=pendulum.length,
+            stroke_color=GREEN,
+        ))
+
+        brace = Brace(Line(ORIGIN, 5 * UP), RIGHT)
+        brace.point = VectorizedPoint(brace.get_right())
+        brace.add(brace.point)
+        brace.set_height(angle)
+        brace.move_to(ORIGIN, DL)
+        brace.apply_complex_function(np.exp)
+        brace.scale(height)
+        brace.rotate(-90 * DEGREES)
+        brace.move_to(arc)
+        brace.shift(MED_SMALL_BUFF * normalize(
+            arc.point_from_proportion(0.5) - top
+        ))
+        x_sym = TexMobject("x")
+        x_sym.set_color(GREEN)
+        x_sym.next_to(brace.point, DR, buff=SMALL_BUFF)
+
+        rhs = TexMobject("=", "L", "\\theta")
+        rhs.set_color_by_tex("\\theta", BLUE)
+        rhs.next_to(x_sym, RIGHT)
+        rhs.shift(0.7 * SMALL_BUFF * UP)
+        line_L = TexMobject("L")
+        line_L.next_to(
+            pendulum.rod.get_center(), UR, SMALL_BUFF,
+        )
+
+        self.play(
+            ShowCreation(arc),
+            Rotate(line, angle, about_point=top),
+            UpdateFromAlphaFunc(
+                line, lambda m, a: m.set_stroke(
+                    width=2 * there_and_back(a)
+                )
+            ),
+            GrowFromPoint(
+                brace, line.get_bottom(),
+                path_arc=angle
+            ),
+        )
+        self.play(FadeInFrom(x_sym, UP))
+        self.wait()
+
+        # Show equation
+        line.set_stroke(BLUE, 5)
+        self.play(
+            ShowCreationThenFadeOut(line),
+            FadeInFromDown(line_L)
+        )
+        self.play(
+            TransformFromCopy(
+                line_L, rhs.get_part_by_tex("L")
+            ),
+            Write(rhs.get_part_by_tex("="))
+        )
+        self.play(
+            TransformFromCopy(
+                pendulum.theta_label,
+                rhs.get_parts_by_tex("\\theta"),
+            )
+        )
+        self.add(rhs)
+
+        x_eq = VGroup(x_sym, rhs)
+
+        self.play(
+            FadeOut(brace),
+            x_eq.rotate, angle / 2,
+            x_eq.next_to, arc.point_from_proportion(0.5),
+            UL, {"buff": -MED_SMALL_BUFF}
+        )
+
+        self.x_eq = x_eq
+        self.arc = arc
+        self.line_L = line_L
+
     def add_g_vect(self):
         pendulum = self.pendulum
 
@@ -927,15 +1137,10 @@ class AnalyzePendulumForce(MovingCameraScene):
             GrowArrow(g_vect),
             FadeInFrom(g_word, UP, lag_ratio=0.1),
         )
+        self.wait()
 
     def show_constraint(self):
         pendulum = self.pendulum
-        weight = pendulum.weight
-        p = weight.get_center()
-        path = CubicBezier([p, p + 3 * DOWN, p + 3 * UP, p])
-
-        self.play(MoveAlongPath(weight, path, run_time=2))
-        self.wait()
 
         arcs = VGroup()
         for u in [-1, 2, -1]:
@@ -946,7 +1151,7 @@ class AnalyzePendulumForce(MovingCameraScene):
                 radius=pendulum.length,
                 arc_center=pendulum.get_fixed_point(),
                 stroke_width=2,
-                stroke_color=GREEN,
+                stroke_color=YELLOW,
                 stroke_opacity=0.5,
             )
             self.play(
@@ -954,9 +1159,7 @@ class AnalyzePendulumForce(MovingCameraScene):
                 ShowCreation(arc)
             )
             arcs.add(arc)
-        self.wait()
-
-        self.traced_arcs = arcs
+        self.play(FadeOut(arcs))
 
     def break_g_vect_into_components(self):
         g_vect = self.g_vect
@@ -983,6 +1186,52 @@ class AnalyzePendulumForce(MovingCameraScene):
         self.play(GrowArrow(g_vect.perp))
         self.wait()
 
+    def show_angle_geometry(self):
+        g_vect = self.g_vect
+
+        arc = Arc(
+            start_angle=90 * DEGREES,
+            angle=self.pendulum.get_theta(),
+            radius=0.5,
+            arc_center=g_vect.get_end(),
+        )
+        q_mark = TexMobject("?")
+        q_mark.next_to(arc.get_center(), UL, SMALL_BUFF)
+        theta_label = TexMobject("\\theta")
+        theta_label.move_to(q_mark)
+
+        self.add(g_vect)
+        self.play(
+            ShowCreation(arc),
+            Write(q_mark)
+        )
+        self.play(ShowCreationThenFadeAround(q_mark))
+        self.wait()
+        self.play(ShowCreationThenFadeAround(
+            self.pendulum.theta_label
+        ))
+        self.play(
+            TransformFromCopy(
+                self.pendulum.theta_label,
+                theta_label,
+            ),
+            FadeOut(q_mark)
+        )
+        self.wait()
+        self.play(WiggleOutThenIn(g_vect.tangent))
+        self.play(WiggleOutThenIn(
+            Line(
+                *g_vect.get_start_and_end(),
+                buff=0,
+            ).add_tip().match_style(g_vect),
+            remover=True
+        ))
+        self.wait()
+        self.play(
+            FadeOut(arc),
+            FadeOut(theta_label),
+        )
+
     def show_gsin_formula(self):
         g_vect = self.g_vect
         g_word = self.g_word
@@ -1037,27 +1286,7 @@ class AnalyzePendulumForce(MovingCameraScene):
         self.g_sin_label = g_sin_label
         self.g_cos_label = g_cos_label
 
-    def show_acceleration_at_different_angles(self):
-        to_fade = VGroup(
-            self.g_cos_label,
-            self.g_vect.perp,
-        )
-        new_comp_line_sytle = {
-            "stroke_width": 0.5,
-            "stroke_opacity": 0.25,
-        }
-
-        self.play(
-            to_fade.set_opacity, 0.25,
-            self.g_vect.component_lines.set_style,
-            new_comp_line_sytle
-        )
-        self.g_vect.component_lines.add_updater(
-            lambda m: m.set_style(**new_comp_line_sytle)
-        )
-        for mob in to_fade:
-            mob.add_updater(lambda m: m.set_opacity(0.25))
-
+    def show_sign(self):
         get_theta = self.pendulum.get_theta
         theta_decimal = DecimalNumber(include_sign=True)
         theta_decimal.add_updater(lambda d: d.set_value(
@@ -1070,84 +1299,148 @@ class AnalyzePendulumForce(MovingCameraScene):
             GREEN if get_theta() > 0 else RED
         ))
 
+        self.play(
+            FadeInFrom(theta_decimal, UP),
+            FadeOut(self.x_eq),
+            FadeOut(self.line_L),
+        )
+        self.set_theta(-60 * DEGREES, run_time=4)
+        self.set_theta(60 * DEGREES, run_time=4)
+        self.play(
+            FadeOut(theta_decimal),
+            FadeIn(self.x_eq),
+        )
+
+    def show_acceleration_formula(self):
+        x_eq = self.x_eq
+        g_sin_theta = self.g_sin_label
+
+        equation = TexMobject(
+            "a", "=",
+            "\\ddot", "x",
+            "=",
+            "-", "g", "\\sin\\big(", "\\theta", "\\big)",
+        )
+        equation.to_edge(LEFT)
+
+        second_deriv = equation[2:4]
+        x_part = equation.get_part_by_tex("x")
+        x_part.set_color(GREEN)
+        a_eq = equation[:2]
+        eq2 = equation.get_parts_by_tex("=")[1]
+        rhs = equation[5:]
+
+        second_deriv_L_form = TexMobject(
+            "L", "\\ddot", "\\theta"
+        )
+        second_deriv_L_form.move_to(second_deriv, DOWN)
+        eq3 = TexMobject("=")
+        eq3.rotate(90 * DEGREES)
+        eq3.next_to(second_deriv_L_form, UP)
+
+        g_L_frac = TexMobject(
+            "-", "{g", "\\over", "L}"
+        )
+        g_L_frac.move_to(rhs[:2], LEFT)
+        g_L_frac.shift(SMALL_BUFF * UP / 2)
+
+        mu_term = TexMobject(
+            "-\\mu", "\\dot", "\\theta",
+        )
+        mu_term.next_to(g_L_frac, LEFT)
+        mu_term.shift(SMALL_BUFF * UP / 2)
+
+        mu_brace = Brace(mu_term, UP)
+        mu_word = mu_brace.get_text("Air resistance")
+
+        for mob in equation, second_deriv_L_form, mu_term:
+            mob.set_color_by_tex("\\theta", BLUE)
+
+        self.play(
+            TransformFromCopy(x_eq[0], x_part),
+            Write(equation[:3]),
+        )
+        self.wait()
+        self.play(
+            Write(eq2),
+            TransformFromCopy(g_sin_theta, rhs)
+        )
+        self.wait()
+        #
+        self.show_acceleration_at_different_angles()
+        #
+        self.play(
+            FadeInFromDown(second_deriv_L_form),
+            Write(eq3),
+            second_deriv.next_to, eq3, UP,
+            a_eq.shift, SMALL_BUFF * LEFT,
+            eq2.shift, SMALL_BUFF * RIGHT,
+            rhs.shift, SMALL_BUFF * RIGHT,
+        )
+        self.wait()
+        self.wait()
+        self.play(
+            FadeOut(a_eq),
+            FadeOut(second_deriv),
+            FadeOut(eq3),
+            ReplacementTransform(
+                second_deriv_L_form.get_part_by_tex("L"),
+                g_L_frac.get_part_by_tex("L"),
+            ),
+            ReplacementTransform(
+                equation.get_part_by_tex("-"),
+                g_L_frac.get_part_by_tex("-"),
+            ),
+            ReplacementTransform(
+                equation.get_part_by_tex("g"),
+                g_L_frac.get_part_by_tex("g"),
+            ),
+            Write(g_L_frac.get_part_by_tex("\\over")),
+            rhs[2:].next_to, g_L_frac, RIGHT, {"buff": SMALL_BUFF},
+        )
+        self.wait()
+        self.play(
+            GrowFromCenter(mu_term),
+            VGroup(eq2, second_deriv_L_form[1:]).next_to,
+            mu_term, LEFT,
+        )
+        self.play(
+            GrowFromCenter(mu_brace),
+            FadeInFromDown(mu_word),
+        )
+
+    def show_acceleration_at_different_angles(self):
+        to_fade = VGroup(
+            self.g_cos_label,
+            self.g_vect.perp,
+        )
+        new_comp_line_sytle = {
+            "stroke_width": 0.5,
+            "stroke_opacity": 0.25,
+        }
+
+        self.play(
+            FadeOut(self.x_eq),
+            to_fade.set_opacity, 0.25,
+            self.g_vect.component_lines.set_style,
+            new_comp_line_sytle
+        )
+        self.g_vect.component_lines.add_updater(
+            lambda m: m.set_style(**new_comp_line_sytle)
+        )
+        for mob in to_fade:
+            mob.add_updater(lambda m: m.set_opacity(0.25))
+
         self.set_theta(0)
         self.wait(2)
         self.set_theta(89.9 * DEGREES, run_time=3)
         self.wait(2)
-        self.set_theta(60 * DEGREES, run_time=2)
-        self.wait()
-
-        self.play(FadeInFrom(theta_decimal, UP))
-        self.set_theta(-60 * DEGREES, run_time=4)
-        self.set_theta(60 * DEGREES, run_time=4)
-        self.play(FadeOut(theta_decimal))
-
-    def show_angle_geometry(self):
-        g_vect = self.g_vect
-        vectors = VGroup(
-            g_vect, g_vect.tangent, g_vect.perp,
-        )
-        g_line = Line(
-            g_vect.get_start(),
-            g_vect.get_end(),
-            stroke_width=1,
-            stroke_color=WHITE,
-        )
-
-        arc = Arc(
-            start_angle=90 * DEGREES,
-            angle=self.pendulum.get_theta(),
-            radius=0.5,
-            arc_center=g_vect.get_end(),
-        )
-        q_mark = TexMobject("?")
-        q_mark.next_to(arc.get_center(), UL, SMALL_BUFF)
-        theta_label = TexMobject("\\theta")
-        theta_label.move_to(q_mark)
-
-        opposite = Line(
-            *g_vect.component_lines[0].get_start_and_end()
-        )
-        adjascent = g_line.copy()
-        opposite.set_stroke(BLUE, 5, opacity=1)
-        adjascent.set_stroke(YELLOW, 5)
-
-        vectors.save_state()
-        vectors.suspend_updating()
-        self.add(g_line, g_vect)
-        self.play(vectors.set_opacity, 0.3)
-        self.play(
-            ShowCreation(arc),
-            Write(q_mark)
-        )
-        self.play(ShowCreationThenFadeAround(q_mark))
-        self.wait()
-        self.play(ShowCreationThenFadeAround(
-            self.pendulum.theta_label
-        ))
-        self.play(
-            TransformFromCopy(
-                self.pendulum.theta_label,
-                theta_label,
-            ),
-            FadeOut(q_mark)
+        self.set_theta(
+            60 * DEGREES,
+            FadeIn(self.x_eq),
+            run_time=2,
         )
         self.wait()
-        self.play(ShowCreation(opposite))
-        self.play(ShowCreation(adjascent))
-        self.wait()
-        self.play(
-            FadeOut(opposite),
-            FadeOut(adjascent),
-        )
-        self.play(
-            Restore(vectors),
-            FadeOut(g_line),
-            FadeOut(arc),
-            FadeOut(theta_label),
-        )
-
-        vectors.resume_updating()
 
     def ask_about_what_to_do(self):
         g_vect = self.g_vect
@@ -1215,103 +1508,22 @@ class AnalyzePendulumForce(MovingCameraScene):
 
         self.play(FocusOn(pendulum.theta_label))
         self.play(Indicate(pendulum.theta_label))
-        old_updaters = pendulum.get_updaters()
-        pendulum.clear_updaters(recursive=False)
-        pendulum.start_swinging()
+
+        pendulum_copy = pendulum.deepcopy()
+        pendulum_copy.clear_updaters()
+        pendulum_copy.fade(1)
+        pendulum_copy.start_swinging()
+
+        def new_updater(p):
+            p.set_theta(pendulum_copy.get_theta())
+        pendulum.add_updater(new_updater)
+
+        self.add(pendulum_copy)
         self.wait(5)
-        pendulum.clear_updaters()
-        for updater in old_updaters:
-            pendulum.add_updater(updater)
-
-    def show_arc_length(self):
-        pendulum = self.pendulum
-        to_fade = VGroup(
-            self.g_vect,
-            self.g_term,
-            self.g_vect.component_lines,
-            self.g_vect.tangent,
-            self.g_vect.perp,
-            self.g_sin_label,
-            self.g_cos_label,
-        )
-        angle = pendulum.get_theta()
-        height = pendulum.length
-        top = pendulum.get_fixed_point()
-
-        line = Line(UP, DOWN)
-        line.set_height(height)
-        line.move_to(top, UP)
-        arc = Arc(
-            start_angle=-90 * DEGREES,
-            angle=angle,
-            arc_center=top,
-            radius=height,
-            stroke_color=GREEN,
-        )
-
-        brace = Brace(Line(ORIGIN, 5 * UP), RIGHT)
-        brace.point = VectorizedPoint(brace.get_right())
-        brace.add(brace.point)
-        brace.set_height(angle)
-        brace.move_to(ORIGIN, DL)
-        brace.apply_complex_function(np.exp)
-        brace.scale(height)
-        brace.rotate(-90 * DEGREES)
-        brace.move_to(arc)
-        brace.shift(MED_SMALL_BUFF * normalize(
-            arc.point_from_proportion(0.5) - top
-        ))
-        x_sym = TexMobject("x")
-        x_sym.set_color(GREEN)
-        x_sym.next_to(brace.point, DR, buff=SMALL_BUFF)
-
-        rhs = TexMobject("=", "L", "\\theta")
-        rhs.set_color_by_tex("\\theta", BLUE)
-        rhs.next_to(x_sym, RIGHT)
-        rhs.shift(0.7 * SMALL_BUFF * UP)
-        line_L = TexMobject("L")
-        line_L.next_to(
-            pendulum.rod.get_center(), UR, SMALL_BUFF,
-        )
-
-        if hasattr(self, "traced_arcs"):
-            self.play(FadeOut(self.traced_arcs))
-        self.play(FadeOut(to_fade))
-        self.play(
-            ShowCreation(arc),
-            Rotate(line, angle, about_point=top),
-            UpdateFromAlphaFunc(
-                line, lambda m, a: m.set_stroke(
-                    width=2 * there_and_back(a)
-                )
-            ),
-            GrowFromPoint(
-                brace, line.get_bottom(),
-                path_arc=angle
-            ),
-        )
-        self.play(FadeInFrom(x_sym, UP))
-        self.wait()
-
-        # Show equation
-        line.set_stroke(BLUE, 5)
-        self.play(
-            ShowCreationThenFadeOut(line),
-            FadeInFromDown(line_L)
-        )
-        self.play(
-            TransformFromCopy(
-                line_L, rhs.get_part_by_tex("L")
-            ),
-            Write(rhs.get_part_by_tex("="))
-        )
-        self.play(
-            TransformFromCopy(
-                pendulum.theta_label,
-                rhs.get_parts_by_tex("\\theta"),
-            )
-        )
-        self.add(rhs)
+        pendulum_copy.end_swinging()
+        self.remove(pendulum_copy)
+        pendulum.remove_updater(new_updater)
+        self.update_mobjects(0)
 
     def show_angular_velocity(self):
         pass
@@ -1664,6 +1876,18 @@ class BuildUpEquation(Scene):
         self.wait()
 
 
+class SimpleDampenedPendulum(Scene):
+    def construct(self):
+        pendulum = Pendulum(
+            top_point=ORIGIN,
+            initial_theta=150 * DEGREES,
+            mu=0.5,
+        )
+        self.add(pendulum)
+        pendulum.start_swinging()
+        self.wait(20)
+
+
 class NewSceneName(Scene):
     def construct(self):
         pass

active_projects/ode/part1/pi_scenes.py

@@ -108,10 +108,37 @@ class FormulasAreLies(PiCreatureScene):
 #         pass
 
 
+class SoWhatIsThetaThen(TeacherStudentsScene):
+    def construct(self):
+        ode = get_ode()
+        ode.to_corner(UL)
+        self.add(ode)
+
+        self.student_says(
+            "Okay, but then\\\\"
+            "what \\emph{is} $\\theta(t)$?"
+        )
+        self.wait()
+        self.play(self.teacher.change, "happy")
+        self.wait(2)
+        self.teacher_says(
+            "First, you must appreciate\\\\"
+            "a deep truth...",
+            added_anims=[self.get_student_changes(
+                *3 * ["confused"]
+            )]
+        )
+        self.wait(4)
+
+
 class ProveTeacherWrong(TeacherStudentsScene):
     def construct(self):
         tex_config = {
-            "tex_to_color_map": {"{\\theta}": BLUE}
+            "tex_to_color_map": {
+                "{\\theta}": BLUE,
+                "{\\dot\\theta}": YELLOW,
+                "{\\ddot\\theta}": RED,
+            }
         }
         func = TexMobject(
             "{\\theta}(t)", "=",
@@ -119,23 +146,24 @@ class ProveTeacherWrong(TeacherStudentsScene):
             **tex_config,
         )
         d_func = TexMobject(
-            "\\dot {\\theta}(t)", "=",
+            "{\\dot\\theta}(t)", "=",
             "-\\left(\\sqrt{g / L}\\right)",
             "\\theta_0", "\\sin(\\sqrt{g / L} \\cdot t)",
             **tex_config,
         )
         dd_func = TexMobject(
-            "\\ddot {\\theta}(t)", "=",
+            "{\\ddot\\theta}(t)", "=",
             "-\\left(g / L\\right)",
             "\\theta_0", "\\cos(\\sqrt{g / L} \\cdot t)",
             **tex_config,
         )
-        ode = TexMobject(
-            "\\ddot {\\theta}({t})", "=",
-            "-\\mu \\dot {\\theta}({t})",
-            "-{g \\over L} \\sin\\big({\\theta}({t})\\big)",
-            **tex_config,
-        )
+        # ode = TexMobject(
+        #     "\\ddot {\\theta}({t})", "=",
+        #     "-\\mu \\dot {\\theta}({t})",
+        #     "-{g \\over L} \\sin\\big({\\theta}({t})\\big)",
+        #     **tex_config,
+        # )
+        ode = get_ode()
         arrows = [TexMobject("\\Downarrow") for x in range(2)]
 
         VGroup(func, d_func, dd_func, ode, *arrows).scale(0.7)
@@ -202,6 +230,58 @@ class ProveTeacherWrong(TeacherStudentsScene):
         self.wait(8)
 
 
+class PhysicistPhaseSpace(PiCreatureScene):
+    def construct(self):
+        physy = self.pi_creature
+        name = TextMobject("Physicist")
+        name.scale(1.5)
+        name.to_corner(DL, buff=MED_SMALL_BUFF)
+        physy.next_to(name, UP, SMALL_BUFF)
+        VGroup(name, physy).shift_onto_screen()
+
+        axes = Axes(
+            x_min=-1,
+            x_max=10,
+            y_min=-1,
+            y_max=7,
+        )
+        axes.set_height(6)
+        axes.next_to(physy, RIGHT)
+        axes.to_edge(UP)
+        axes.set_stroke(width=1)
+        x_label = TextMobject("Position")
+        x_label.next_to(axes.x_axis.get_right(), UP)
+        y_label = TextMobject("Momentum")
+        y_label.next_to(axes.y_axis.get_top(), RIGHT)
+
+        title = TextMobject("Phase space")
+        title.scale(1.5)
+        title.set_color(YELLOW)
+        title.move_to(axes)
+
+        self.add(name, physy)
+
+        self.play(
+            physy.change, "angry",
+            Write(axes),
+            FadeInFromDown(title)
+        )
+        self.wait(2)
+        self.play(
+            GrowFromPoint(x_label, physy.get_corner(UR)),
+            physy.change, "raise_right_hand",
+            axes.x_axis.get_right()
+        )
+        self.play(
+            GrowFromPoint(y_label, physy.get_corner(UR)),
+            physy.look_at, axes.y_axis.get_top(),
+        )
+        self.wait(3)
+
+    def create_pi_creature(self):
+        return PiCreature(color=GREY).to_corner(DL)
+
+
 class AskAboutActuallySolving(TeacherStudentsScene):
     def construct(self):
         ode = get_ode()
@@ -211,7 +291,7 @@ class AskAboutActuallySolving(TeacherStudentsScene):
 
         self.student_says(
             "Yeah yeah, but how do\\\\"
-            "you acutally \\emph{solve} it?",
+            "you actually \\emph{solve} it?",
             student_index=1,
             target_mode="sassy",
             added_anims=[morty.change, "thinking"],
@@ -242,9 +322,7 @@ class HungerForExactness(TeacherStudentsScene):
         ode.to_corner(UL)
         left_part = ode[:5]
         friction_part = ode[5:11]
-        right_part = ode[11:]
         self.add(ode)
-        frictionless_group = VGroup(left_part, right_part)
 
         proposed_solution = TexMobject(
             "\\theta_0\\cos((\\sqrt{g/L})t)e^{-\\mu t}"
@@ -376,9 +454,62 @@ class HungerForExactness(TeacherStudentsScene):
             )
             self.wait()
         self.wait(3)
+        self.change_student_modes("tired", "sad", "concerned_musician")
+        self.wait(4)
+        self.look_at(solution)
+        self.wait(5)
         self.play(
             FadeOutAndShift(solution, 2 * LEFT),
             Restore(ode),
-            self.get_student_changes(*3 * ["sick"])
+            self.get_student_changes(
+                "sick", "angry", "tired",
+            )
         )
         self.wait(3)
+
+        mystery = TexMobject(
+            "\\theta(t) = ???",
+            tex_to_color_map={"\\theta": BLUE},
+        )
+        mystery.scale(2)
+        mystery.to_edge(UP)
+        mystery.set_stroke(width=0, background=True)
+        mystery_boundary = AnimatedBoundary(
+            mystery, stroke_width=1
+        )
+
+        self.play(
+            FadeInFromDown(mystery),
+            self.teacher.change, "pondering"
+        )
+        self.add(mystery_boundary, mystery)
+        self.change_all_student_modes("sad")
+        self.look_at(mystery)
+        self.wait(5)
+
+        # Define
+        self.student_says(
+            "Let $\\text{P}(\\mu, g, L; t)$ be a\\\\"
+            "function satisfying this ODE.",
+            student_index=0,
+            target_mode="speaking",
+            added_anims=[
+                FadeOut(mystery),
+                FadeOut(mystery_boundary),
+                ode.to_corner, UR
+            ]
+        )
+        self.change_student_modes(
+            "hooray", "sassy", "sassy",
+            look_at_arg=students[0].eyes.get_corner(UR),
+        )
+        self.wait(2)
+
+
+class ItGetsWorse(TeacherStudentsScene):
+    def construct(self):
+        self.teacher_says("It gets\\\\worse")
+        self.change_student_modes(
+            "hesitant", "pleading", "erm"
+        )
+        self.wait(5)

active_projects/ode/part1/shared_constructs.py

@@ -20,8 +20,8 @@ def get_ode():
     tex_config = {
         "tex_to_color_map": {
             "{\\theta}": BLUE,
-            "{\\dot\\theta}": YELLOW,
-            "{\\ddot\\theta}": RED,
+            "{\\dot\\theta}": RED,
+            "{\\ddot\\theta}": YELLOW,
             "{t}": WHITE,
             "{\\mu}": WHITE,
         }
@@ -35,6 +35,16 @@ def get_ode():
     return ode
 
 
+def get_period_formula():
+    return TexMobject(
+        "2\\pi", "\\sqrt{\\,", "L", "/", "g", "}",
+        tex_to_color_map={
+            "L": BLUE,
+            "g": YELLOW,
+        }
+    )
+
+
 def pendulum_vector_field_func(point, mu=0.1, g=9.8, L=3):
     theta, omega = point[:2]
     return np.array([
@@ -54,3 +64,55 @@ def get_vector_symbol(*texs, **kwargs):
     config.update(kwargs)
     array = [[tex] for tex in texs]
     return Matrix(array, **config)
+
+
+def get_heart_var(index):
+    heart = SuitSymbol("hearts")
+    if index == 1:
+        heart.set_color(BLUE_C)
+    elif index == 2:
+        heart.set_color(GREEN)
+    heart.set_height(0.7)
+    index = Integer(index)
+    index.move_to(heart.get_corner(DR))
+    heart.add(index)
+    return heart
+
+
+def get_heart_var_deriv(index):
+    heart = get_heart_var(index)
+    filler_tex = "T"
+    deriv = TexMobject("{d", filler_tex, "\\over", "dt}")
+    deriv.scale(2)
+    filler = deriv.get_part_by_tex(filler_tex)
+    heart.match_height(filler)
+    heart.move_to(filler)
+    heart.scale(1.5, about_edge=UL)
+    deriv.remove(filler)
+    deriv.add(heart)
+    deriv.heart = heart
+    return deriv
+
+
+def get_love_equation1():
+    equation = VGroup(
+        get_heart_var_deriv(1),
+        TexMobject("=").scale(2),
+        TexMobject("a").scale(2),
+        get_heart_var(2)
+    )
+    equation.arrange(RIGHT)
+    equation[-1].shift(SMALL_BUFF * DL)
+    return equation
+
+
+def get_love_equation2():
+    equation = VGroup(
+        get_heart_var_deriv(2),
+        TexMobject("=").scale(2),
+        TexMobject("-b").scale(2),
+        get_heart_var(1),
+    )
+    equation.arrange(RIGHT)
+    equation[-1].shift(SMALL_BUFF * DL)
+    return equation

active_projects/ode/part1/wordy_scenes.py

@@ -37,6 +37,40 @@ class SmallAngleApproximationTex(Scene):
 
 class StrogatzQuote(Scene):
     def construct(self):
+        quote = self.get_quote()
+        movers = VGroup(*quote[:-1].family_members_with_points())
+        for mover in movers:
+            mover.save_state()
+            disc = Circle(radius=0.05)
+            disc.set_stroke(width=0)
+            disc.set_fill(BLACK, 0)
+            disc.move_to(mover)
+            mover.become(disc)
+        self.play(
+            FadeInFrom(quote.author_part, LEFT),
+            LaggedStartMap(
+                # FadeInFromLarge,
+                # quote[:-1].family_members_with_points(),
+                Restore, movers,
+                lag_ratio=0.005,
+                run_time=2,
+            )
+            # FadeInFromDown(quote[:-1]),
+            # lag_ratio=0.01,
+        )
+        self.wait()
+        self.play(
+            Write(quote.law_part.copy().set_color(YELLOW)),
+            run_time=1,
+        )
+        self.wait()
+        self.play(
+            Write(quote.language_part.copy().set_color(BLUE)),
+            run_time=1.5,
+        )
+        self.wait(2)
+
+    def get_quote(self):
         law_words = "laws of physics"
         language_words = "language of differential equations"
         author = "-Steven Strogatz"
@@ -51,47 +85,342 @@ class StrogatzQuote(Scene):
             arg_separator=" ",
             substrings_to_isolate=[law_words, language_words, author]
         )
-        law_part = quote.get_part_by_tex(law_words)
-        language_part = quote.get_part_by_tex(language_words)
-        author_part = quote.get_part_by_tex(author)
+        quote.law_part = quote.get_part_by_tex(law_words)
+        quote.language_part = quote.get_part_by_tex(language_words)
+        quote.author_part = quote.get_part_by_tex(author)
         quote.set_width(12)
         quote.to_edge(UP)
         quote[-2].shift(SMALL_BUFF * LEFT)
-        author_part.shift(RIGHT + 0.5 * DOWN)
-        author_part.scale(1.2, about_edge=UL)
+        quote.author_part.shift(RIGHT + 0.5 * DOWN)
+        quote.author_part.scale(1.2, about_edge=UL)
 
-        movers = VGroup(*quote[:-1].family_members_with_points())
-        for mover in movers:
-            mover.save_state()
-            disc = Circle(radius=0.05)
-            disc.set_stroke(width=0)
-            disc.set_fill(BLACK, 0)
-            disc.move_to(mover)
-            mover.become(disc)
-        self.play(
-            FadeInFrom(author_part, LEFT),
-            LaggedStartMap(
-                # FadeInFromLarge,
-                # quote[:-1].family_members_with_points(),
-                Restore, movers,
-                lag_ratio=0.005,
-                run_time=2,
+        return quote
+
+
+class WriteInRadians(Scene):
+    def construct(self):
+        words = TextMobject("In radians")
+        words.set_color(YELLOW)
+        square = SurroundingRectangle(TexMobject("\\theta"))
+        square.next_to(words, UP)
+        self.play(ShowCreation(square))
+        self.play(Write(words), FadeOut(square))
+        self.wait()
+
+
+class XEqLThetaToCorner(Scene):
+    def construct(self):
+        equation = TexMobject(
+            "x = L\\theta",
+            tex_to_color_map={
+                "x": GREEN,
+                "\\theta": BLUE,
+            }
         )
-            # FadeInFromDown(quote[:-1]),
-            # lag_ratio=0.01,
+        equation.move_to(DOWN + 3 * RIGHT)
+        self.add(equation)
+        self.play(equation.to_corner, DL, {"buff": LARGE_BUFF})
+        self.wait()
+
+
+class ComingUp(Scene):
+    CONFIG = {
+        "camera_config": {"background_color": DARKER_GREY}
+    }
+
+    def construct(self):
+        frame = ScreenRectangle(
+            stroke_width=0,
+            fill_color=BLACK,
+            fill_opacity=1,
+            height=6
+        )
+        title = TextMobject("Coming up")
+        title.scale(1.5)
+        title.to_edge(UP)
+        frame.next_to(title, DOWN)
+        animated_frame = AnimatedBoundary(frame)
+        self.add(frame, title, animated_frame)
+        self.wait(10)
+
+
+class InputLabel(Scene):
+    def construct(self):
+        label = TextMobject("Input")
+        label.scale(1.25)
+        arrow = Vector(UP)
+        arrow.next_to(label, UP)
+        self.play(
+            FadeInFrom(label, UP),
+            GrowArrow(arrow)
+        )
+        self.wait()
+
+
+class ReallyHardToSolve(Scene):
+    def construct(self):
+        words = TextMobject(
+            "They're", "really\\\\",
+            "freaking", "hard\\\\",
+            "to", "solve\\\\",
+        )
+        words.set_height(6)
+
+        self.wait()
+        for word in words:
+            wait_time = 0.05 * len(word)
+            self.add(word)
+            self.wait(wait_time)
+        self.wait()
+
+
+class ReasonForSolution(Scene):
+    def construct(self):
+        # Words
+        eq_word = TextMobject("Differential\\\\Equation")
+        s_word = TextMobject("Solution")
+        u_word = TextMobject("Understanding")
+        c_word = TextMobject("Computation")
+        cu_group = VGroup(u_word, c_word)
+        cu_group.arrange(DOWN, buff=2)
+        group = VGroup(eq_word, s_word, cu_group)
+        group.arrange(RIGHT, buff=2)
+        words = VGroup(eq_word, s_word, u_word, c_word)
+
+        # Arrows
+        arrows = VGroup(
+            Arrow(eq_word.get_right(), s_word.get_left()),
+            Arrow(s_word.get_right(), u_word.get_left()),
+            Arrow(s_word.get_right(), c_word.get_left()),
+        )
+        arrows.set_color(LIGHT_GREY)
+        new_arrows = VGroup(
+            Arrow(
+                eq_word.get_corner(UR),
+                u_word.get_left(),
+                path_arc=-60 * DEGREES,
+            ),
+            Arrow(
+                eq_word.get_corner(DR),
+                c_word.get_left(),
+                path_arc=60 * DEGREES,
+            ),
+        )
+        new_arrows.set_color(BLUE)
+
+        # Define first examples
+        t2c = {
+            "{x}": BLUE,
+            "{\\dot x}": RED,
+        }
+        equation = TexMobject(
+            "{\\dot x}(t) = k {x}(t)",
+            tex_to_color_map=t2c,
+        )
+        equation.next_to(eq_word, DOWN)
+        solution = TexMobject(
+            "{x}(t) = x_0 e^{kt}",
+            tex_to_color_map=t2c,
+        )
+        solution.next_to(s_word, DOWN, MED_LARGE_BUFF)
+        equation.align_to(solution, DOWN)
+
+        axes = Axes(
+            x_min=-1,
+            x_max=5.5,
+            y_min=-1,
+            y_max=4.5,
+            y_axis_config={"unit_size": 0.5}
+        )
+        axes.set_stroke(width=2)
+        graph_line = axes.get_graph(
+            lambda x: np.exp(0.4 * x)
+        )
+        graph_line.set_stroke(width=2)
+        graph = VGroup(axes, graph_line)
+        graph.scale(0.5)
+        graph.next_to(u_word, UP)
+
+        computation = TexMobject(
+            # "\\displaystyle "
+            "e^x = \\sum_{n=0}^\\infty "
+            "\\frac{x^n}{n!}"
+        )
+        computation.next_to(c_word, DOWN)
+
+        first_examples = VGroup(
+            equation, solution, graph, computation
+        )
+
+        # Second example
+        ode = get_ode()
+        ode.scale(0.75)
+        second_examples = VGroup(
+            ode,
+            TexMobject("???").set_color(LIGHT_GREY),
+            ScreenRectangle(
+                height=2,
+                stroke_width=1,
+            ),
+        )
+        for fe, se in zip(first_examples, second_examples):
+            se.move_to(fe, DOWN)
+
+        ode.shift(2 * SMALL_BUFF * DOWN)
+        ode.add_to_back(BackgroundRectangle(ode[-4:]))
+
+        self.add(eq_word)
+        self.add(equation)
+        self.play(
+            FadeInFrom(s_word, LEFT),
+            GrowArrow(arrows[0]),
+            TransformFromCopy(equation, solution)
         )
         self.wait()
         self.play(
-            Write(law_part.copy().set_color(YELLOW)),
-            run_time=1,
+            FadeInFrom(c_word, UL),
+            GrowArrow(arrows[2]),
+            FadeInFrom(computation, UP)
         )
         self.wait()
         self.play(
-            Write(language_part.copy().set_color(BLUE)),
-            run_time=1.5,
+            FadeInFrom(u_word, DL),
+            GrowArrow(arrows[1]),
+            FadeInFromDown(graph)
         )
         self.wait(2)
 
+        self.play(
+            FadeOut(first_examples),
+            FadeIn(second_examples[:2])
+        )
+        self.wait()
+        self.play(
+            arrows.fade, 0.75,
+            s_word.fade, 0.75,
+            second_examples[1].fade, 0.75,
+            ShowCreation(new_arrows[0]),
+            FadeIn(second_examples[2])
+        )
+        self.play(
+            ShowCreation(new_arrows[1]),
+            Animation(second_examples),
+        )
+        self.wait()
+
+
+class WritePhaseSpace(Scene):
+    def construct(self):
+        word = TextMobject("Phase space")
+        word.scale(2)
+        word.shift(FRAME_WIDTH * LEFT / 4)
+        word.to_edge(UP)
+        word.add_background_rectangle()
+
+        lines = VGroup(*[
+            Line(v, 1.3 * v)
+            for v in compass_directions(50)
+        ])
+        lines.replace(word, stretch=True)
+        lines.scale(1.5)
+        lines.set_stroke(YELLOW)
+        lines.shuffle()
+
+        self.add(word)
+        self.play(
+            ShowPassingFlashWithThinningStrokeWidth(
+                lines,
+                lag_ratio=0.002,
+                run_time=1.5,
+                time_width=0.9,
+                n_segments=5,
+            )
+        )
+        self.wait()
+
+
+class GleickQuote(Scene):
+    def construct(self):
+        quote = TextMobject(
+            "``[Phase space is] one of the most\\\\",
+            "powerful inventions", "of modern science.''\\\\",
+        )
+        quote.power_part = quote.get_part_by_tex("power")
+        book = ImageMobject("ChaosBookCover")
+        book.set_height(5)
+        book.next_to(ORIGIN, LEFT)
+        book.to_edge(DOWN)
+        gleick = ImageMobject("JamesGleick")
+        gleick.set_height(5)
+        gleick.next_to(ORIGIN, RIGHT)
+        gleick.to_edge(DOWN)
+        quote.to_edge(UP)
+
+        self.play(
+            FadeInFrom(book, RIGHT),
+            FadeInFrom(gleick, LEFT),
+        )
+        self.wait()
+        self.play(Write(quote))
+        self.play(Write(
+            quote.power_part.copy().set_color(BLUE),
+            run_time=1
+        ))
+        self.wait()
+
+
+class WritePhaseFlow(Scene):
+    def construct(self):
+        words = TextMobject("Phase flow")
+        words.scale(2)
+        words.shift(FRAME_WIDTH * LEFT / 4)
+        words.to_edge(UP)
+        words.add_background_rectangle()
+        self.play(Write(words))
+        self.wait()
+
+
+class ShowSineValues(Scene):
+    def construct(self):
+        angle_tracker = ValueTracker(60 * DEGREES)
+        get_angle = angle_tracker.get_value
+        formula = always_redraw(
+            lambda: self.get_sine_formula(get_angle())
+        )
+        self.add(formula)
+
+        self.play(
+            angle_tracker.set_value, 0,
+            run_time=3,
+        )
+        self.wait()
+        self.play(
+            angle_tracker.set_value, 90 * DEGREES,
+            run_time=3,
+        )
+        self.wait()
+
+    def get_sine_formula(self, angle):
+        sin, lp, rp = TexMobject(
+            "\\sin", "(", ") = "
+        )
+        input_part = Integer(
+            angle / DEGREES,
+            unit="^\\circ",
+        )
+        input_part.set_color(YELLOW)
+        output_part = DecimalNumber(
+            np.sin(input_part.get_value() * DEGREES),
+            num_decimal_places=3,
+        )
+        result = VGroup(
+            sin, lp, input_part, rp, output_part
+        )
+        result.arrange(RIGHT, buff=SMALL_BUFF)
+        sin.scale(1.1, about_edge=DOWN)
+        lp.align_to(rp, UP)
+        return result
+
 
 class SetAsideSeekingSolution(Scene):
     def construct(self):
@@ -141,6 +470,14 @@ class SetAsideSeekingSolution(Scene):
         )
 
 
+class ThreeBodyTitle(Scene):
+    def construct(self):
+        title = TextMobject("Three body problem")
+        title.scale(1.5)
+        title.to_edge(UP)
+        self.add(title)
+
+
 class ThreeBodySymbols(Scene):
     def construct(self):
         self.init_coord_groups()
@@ -260,3 +597,259 @@ class ThreeBodySymbols(Scene):
             rate_func=linear,
         )
         self.play(FadeOut(coord_copies))
+
+
+class ThreeBodyEquation(Scene):
+    def construct(self):
+        x1 = "\\vec{\\textbf{x}}_1"
+        x2 = "\\vec{\\textbf{x}}_2"
+        x3 = "\\vec{\\textbf{x}}_3"
+        kw = {
+            "tex_to_color_map": {
+                x1: RED,
+                x2: GREEN,
+                x3: BLUE,
+            }
+        }
+        equations = VGroup(*[
+            TexMobject(
+                "{d^2", t1, "\\over dt^2}", "=",
+                "G", "\\left("
+                "{" + m2, "(", t2, "-", t1, ")"
+                "\\over"
+                "||", t2, "-", t1, "||^3}",
+                "+",
+                "{" + m3, "(", t3, "-", t1, ")"
+                "\\over"
+                "||", t3, "-", t1, "||^3}",
+                "\\right)",
+                **kw
+            )
+            for t1, t2, t3, m1, m2, m3 in [
+                (x1, x2, x3, "m_1", "m_2", "m_3"),
+                (x2, x3, x1, "m_2", "m_3", "m_1"),
+                (x3, x1, x2, "m_3", "m_1", "m_2"),
+            ]
+        ])
+        equations.arrange(DOWN, buff=LARGE_BUFF)
+
+        self.play(LaggedStartMap(
+            FadeInFrom, equations,
+            lambda m: (m, UP),
+            lag_ratio=0.2,
+        ))
+        self.wait()
+
+
+class JumpToThisPoint(Scene):
+    def construct(self):
+        dot = Dot(color=YELLOW)
+        dot.scale(0.5)
+
+        arrow = Vector(DR, color=WHITE)
+        arrow.next_to(dot, UL, SMALL_BUFF)
+        words = TextMobject(
+            "Jump directly to\\\\",
+            "this point?",
+        )
+        words.add_background_rectangle_to_submobjects()
+        words.next_to(arrow.get_start(), UP, SMALL_BUFF)
+
+        self.play(
+            FadeInFromLarge(dot, 20),
+            rate_func=rush_into,
+        )
+        self.play(
+            GrowArrow(arrow),
+            FadeInFromDown(words),
+        )
+
+
+class ChaosTitle(Scene):
+    def construct(self):
+        title = TextMobject("Chaos theory")
+        title.scale(1.5)
+        title.to_edge(UP)
+        line = Line(LEFT, RIGHT)
+        line.set_width(FRAME_WIDTH - 1)
+        line.next_to(title, DOWN)
+
+        self.play(
+            Write(title),
+            ShowCreation(line),
+        )
+        self.wait()
+
+
+class RevisitQuote(StrogatzQuote, PiCreatureScene):
+    def construct(self):
+        quote = self.get_quote()
+        quote.law_part.set_color(YELLOW)
+        quote.language_part.set_color(BLUE)
+        quote.set_stroke(BLACK, 6, background=True)
+        quote.scale(0.8, about_edge=UL)
+
+        new_langauge_part = TextMobject(
+            "\\Large Language of differential equations"
+        )
+        new_langauge_part.to_edge(UP)
+        new_langauge_part.match_style(quote.language_part)
+
+        randy = self.pi_creature
+
+        self.play(
+            FadeInFrom(quote[:-1], DOWN),
+            FadeInFrom(quote[-1:], LEFT),
+            randy.change, "raise_right_hand",
+        )
+        self.play(Blink(randy))
+        self.play(randy.change, "angry")
+        self.play(
+            Blink(randy),
+            VFadeOut(randy, run_time=3)
+        )
+        mover = VGroup(quote.language_part)
+        self.add(quote, mover)
+        self.play(
+            ReplacementTransform(
+                mover, new_langauge_part,
+            ),
+            *[
+                FadeOut(part)
+                for part in quote
+                if part is not quote.language_part
+            ],
+            run_time=2,
+        )
+        self.wait()
+
+
+class EndScreen(PatreonEndScreen):
+    CONFIG = {
+        "specific_patrons": [
+            "Juan Benet",
+            "Vassili Philippov",
+            "Burt Humburg",
+            "Carlos Vergara Del Rio",
+            "Matt Russell",
+            "Scott Gray",
+            "soekul",
+            "Tihan Seale",
+            "Ali Yahya",
+            "dave nicponski",
+            "Evan Phillips",
+            "Graham",
+            "Joseph Kelly",
+            "Kaustuv DeBiswas",
+            "LambdaLabs",
+            "Lukas Biewald",
+            "Mike Coleman",
+            "Peter Mcinerney",
+            "Quantopian",
+            "Roy Larson",
+            "Scott Walter, Ph.D.",
+            "Yana Chernobilsky",
+            "Yu Jun",
+            "Jordan Scales",
+            "Lukas -krtek.net- Novy",
+            "John Shaughnessy",
+            "Britt Selvitelle",
+            "David Gow",
+            "J",
+            "Jonathan Wilson",
+            "Joseph John Cox",
+            "Magnus Dahlström",
+            "Randy C. Will",
+            "Ryan Atallah",
+            "Luc Ritchie",
+            "1stViewMaths",
+            "Adrian Robinson",
+            "Alexis Olson",
+            "Andreas Benjamin Brössel",
+            "Andrew Busey",
+            "Ankalagon",
+            "Antonio Juarez",
+            "Arjun Chakroborty",
+            "Art Ianuzzi",
+            "Awoo",
+            "Bernd Sing",
+            "Boris Veselinovich",
+            "Brian Staroselsky",
+            "Chad Hurst",
+            "Charles Southerland",
+            "Chris Connett",
+            "Christian Kaiser",
+            "Clark Gaebel",
+            "Cooper Jones",
+            "Danger Dai",
+            "Dave B",
+            "Dave Kester",
+            "David Clark",
+            "DeathByShrimp",
+            "Delton Ding",
+            "eaglle",
+            "emptymachine",
+            "Eric Younge",
+            "Eryq Ouithaqueue",
+            "Federico Lebron",
+            "Giovanni Filippi",
+            "Hal Hildebrand",
+            "Herman Dieset",
+            "Hitoshi Yamauchi",
+            "Isaac Jeffrey Lee",
+            "j eduardo perez",
+            "Jacob Magnuson",
+            "Jameel Syed",
+            "Jason Hise",
+            "Jeff Linse",
+            "Jeff Straathof",
+            "John Griffith",
+            "John Haley",
+            "John V Wertheim",
+            "Jonathan Eppele",
+            "Kai-Siang Ang",
+            "Kanan Gill",
+            "L0j1k",
+            "Lee Redden",
+            "Linh Tran",
+            "Ludwig Schubert",
+            "Magister Mugit",
+            "Mark B Bahu",
+            "Mark Heising",
+            "Martin Price",
+            "Mathias Jansson",
+            "Matt Langford",
+            "Matt Roveto",
+            "Matthew Cocke",
+            "Michael Faust",
+            "Michael Hardel",
+            "Mirik Gogri",
+            "Mustafa Mahdi",
+            "Márton Vaitkus",
+            "Nero Li",
+            "Nikita Lesnikov",
+            "Omar Zrien",
+            "Owen Campbell-Moore",
+            "Peter Ehrnstrom",
+            "RedAgent14",
+            "rehmi post",
+            "Richard Burgmann",
+            "Richard Comish",
+            "Ripta Pasay",
+            "Rish Kundalia",
+            "Robert Teed",
+            "Roobie",
+            "Ryan Williams",
+            "Samuel D. Judge",
+            "Solara570",
+            "Stevie Metke",
+            "Tal Einav",
+            "Ted Suzman",
+            "Valeriy Skobelev",
+            "Xavier Bernard",
+            "Yavor Ivanov",
+            "Yaw Etse",
+            "YinYangBalance.Asia",
+            "Zach Cardwell",
+        ]
+    }

active_projects/ode/part2/fourier_series.py

@@ -0,0 +1,518 @@
+from big_ol_pile_of_manim_imports import *
+# import scipy
+
+
+class FourierCirclesScene(Scene):
+    CONFIG = {
+        "n_circles": 10,
+        "big_radius": 2,
+        "colors": [
+            BLUE_D,
+            BLUE_C,
+            BLUE_E,
+            GREY_BROWN,
+        ],
+        "circle_style": {
+            "stroke_width": 2,
+        },
+        "base_frequency": 1,
+        "slow_factor": 0.25,
+        "center_point": ORIGIN,
+        "parametric_function_step_size": 0.001,
+    }
+
+    #
+    def get_freqs(self):
+        n = self.n_circles
+        all_freqs = list(range(n // 2, -n // 2, -1))
+        all_freqs.sort(key=abs)
+        return all_freqs
+
+    def get_coefficients(self):
+        return [complex(0) for x in range(self.n_circles)]
+
+    def get_color_iterator(self):
+        return it.cycle(self.colors)
+
+    def get_circles(self, freqs=None, coefficients=None):
+        circles = VGroup()
+        color_iterator = self.get_color_iterator()
+        self.center_tracker = VectorizedPoint(self.center_point)
+
+        if freqs is None:
+            freqs = self.get_freqs()
+        if coefficients is None:
+            coefficients = self.get_coefficients()
+
+        last_circle = None
+        for freq, coefficient in zip(freqs, coefficients):
+            if last_circle:
+                center_func = last_circle.get_start
+            else:
+                center_func = self.center_tracker.get_location
+            circle = self.get_circle(
+                coefficient=coefficient,
+                freq=freq,
+                color=next(color_iterator),
+                center_func=center_func,
+            )
+            circles.add(circle)
+            last_circle = circle
+        return circles
+
+    def get_circle(self, coefficient, freq, color, center_func):
+        radius = abs(coefficient)
+        phase = np.log(coefficient).imag
+        circle = Circle(
+            radius=radius,
+            color=color,
+            **self.circle_style,
+        )
+        circle.radial_line = Line(
+            circle.get_center(),
+            circle.get_start(),
+            color=WHITE,
+            **self.circle_style,
+        )
+        circle.add(circle.radial_line)
+        circle.freq = freq
+        circle.phase = phase
+        circle.rotate(phase)
+        circle.coefficient = coefficient
+        circle.center_func = center_func
+        circle.add_updater(self.update_circle)
+        return circle
+
+    def update_circle(self, circle, dt):
+        circle.rotate(
+            self.slow_factor * circle.freq * dt * TAU
+        )
+        circle.move_to(circle.center_func())
+        return circle
+
+    def get_rotating_vectors(self, circles):
+        return VGroup(*[
+            self.get_rotating_vector(circle)
+            for circle in circles
+        ])
+
+    def get_rotating_vector(self, circle):
+        vector = Vector(RIGHT, color=WHITE)
+        vector.add_updater(lambda v: v.put_start_and_end_on(
+            *circle.radial_line.get_start_and_end()
+        ))
+        return vector
+
+    def get_circle_end_path(self, circles, color=YELLOW):
+        coefs = [c.coefficient for c in circles]
+        freqs = [c.freq for c in circles]
+        center = circles[0].get_center()
+
+        path = ParametricFunction(
+            lambda t: center + reduce(op.add, [
+                complex_to_R3(
+                    coef * np.exp(TAU * 1j * freq * t)
+                )
+                for coef, freq in zip(coefs, freqs)
+            ]),
+            t_min=0,
+            t_max=1,
+            color=color,
+            step_size=self.parametric_function_step_size,
+        )
+        return path
+
+    # TODO, this should be a general animated mobect
+    def get_drawn_path(self, circles, **kwargs):
+        path = self.get_circle_end_path(circles, **kwargs)
+        broken_path = CurvesAsSubmobjects(path)
+        broken_path.curr_time = 0
+
+        def update_path(path, dt):
+            alpha = path.curr_time * self.slow_factor
+            n_curves = len(path)
+            for a, sp in zip(np.linspace(0, 1, n_curves), path):
+                b = alpha - a
+                if b < 0:
+                    width = 0
+                else:
+                    width = 2 * (1 - (b % 1))
+                sp.set_stroke(YELLOW, width=width)
+            path.curr_time += dt
+            return path
+
+        broken_path.add_updater(update_path)
+        return broken_path
+
+    def get_y_component_wave(self,
+                             circles,
+                             left_x=1,
+                             color=PINK,
+                             n_copies=2,
+                             right_shift_rate=5):
+        path = self.get_circle_end_path(circles)
+        wave = ParametricFunction(
+            lambda t: op.add(
+                right_shift_rate * t * LEFT,
+                path.function(t)[1] * UP
+            ),
+            t_min=path.t_min,
+            t_max=path.t_max,
+            color=color,
+        )
+        wave_copies = VGroup(*[
+            wave.copy()
+            for x in range(n_copies)
+        ])
+        wave_copies.arrange(RIGHT, buff=0)
+        top_point = wave_copies.get_top()
+        wave.creation = ShowCreation(
+            wave,
+            run_time=(1 / self.slow_factor),
+            rate_func=linear,
+        )
+        cycle_animation(wave.creation)
+        wave.add_updater(lambda m: m.shift(
+            (m.get_left()[0] - left_x) * LEFT
+        ))
+
+        def update_wave_copies(wcs):
+            index = int(
+                wave.creation.total_time * self.slow_factor
+            )
+            wcs[:index].match_style(wave)
+            wcs[index:].set_stroke(width=0)
+            wcs.next_to(wave, RIGHT, buff=0)
+            wcs.align_to(top_point, UP)
+        wave_copies.add_updater(update_wave_copies)
+
+        return VGroup(wave, wave_copies)
+
+    def get_wave_y_line(self, circles, wave):
+        return DashedLine(
+            circles[-1].get_start(),
+            wave[0].get_end(),
+            stroke_width=1,
+            dash_length=DEFAULT_DASH_LENGTH * 0.5,
+        )
+
+    # Computing Fourier series
+    def get_coefficients_of_path(self, path, n_samples=10000, freqs=None):
+        if freqs is None:
+            freqs = self.get_freqs()
+        dt = 1 / n_samples
+        ts = np.arange(0, 1, dt)
+        samples = np.array([
+            path.point_from_proportion(t)
+            for t in ts
+        ])
+        samples -= self.center_point
+        complex_samples = samples[:, 0] + 1j * samples[:, 1]
+
+        result = []
+        for freq in freqs:
+            riemann_sum = np.array([
+                np.exp(-TAU * 1j * freq * t) * cs
+                for t, cs in zip(ts, complex_samples)
+            ]).sum() * dt
+            result.append(riemann_sum)
+
+        return result
+
+
+class FourierSeriesIntroBackground4(FourierCirclesScene):
+    CONFIG = {
+        "n_circles": 4,
+        "center_point": 4 * LEFT,
+        "run_time": 30,
+        "big_radius": 1.5,
+    }
+
+    def construct(self):
+        circles = self.get_circles()
+        path = self.get_drawn_path(circles)
+        wave = self.get_y_component_wave(circles)
+        h_line = always_redraw(
+            lambda: self.get_wave_y_line(circles, wave)
+        )
+
+        # Why?
+        circles.update(-1 / self.camera.frame_rate)
+        #
+        self.add(circles, path, wave, h_line)
+        self.wait(self.run_time)
+
+    def get_ks(self):
+        return np.arange(1, 2 * self.n_circles + 1, 2)
+
+    def get_freqs(self):
+        return self.base_frequency * self.get_ks()
+
+    def get_coefficients(self):
+        return self.big_radius / self.get_ks()
+
+
+class FourierSeriesIntroBackground8(FourierSeriesIntroBackground4):
+    CONFIG = {
+        "n_circles": 8,
+    }
+
+
+class FourierSeriesIntroBackground12(FourierSeriesIntroBackground4):
+    CONFIG = {
+        "n_circles": 12,
+    }
+
+
+class FourierSeriesIntroBackground20(FourierSeriesIntroBackground4):
+    CONFIG = {
+        "n_circles": 20,
+    }
+
+
+class FourierOfPiSymbol(FourierCirclesScene):
+    CONFIG = {
+        "n_circles": 50,
+        "center_point": ORIGIN,
+        "slow_factor": 0.1,
+        "run_time": 30,
+        "tex": "\\pi",
+        "start_drawn": False,
+    }
+
+    def construct(self):
+        path = self.get_path()
+        coefs = self.get_coefficients_of_path(path)
+
+        circles = self.get_circles(coefficients=coefs)
+        for k, circle in zip(it.count(1), circles):
+            circle.set_stroke(width=max(
+                1 / np.sqrt(k),
+                1,
+            ))
+
+        # approx_path = self.get_circle_end_path(circles)
+        drawn_path = self.get_drawn_path(circles)
+        if self.start_drawn:
+            drawn_path.curr_time = 1 / self.slow_factor
+
+        self.add(path)
+        self.add(circles)
+        self.add(drawn_path)
+        self.wait(self.run_time)
+
+    def get_path(self):
+        tex_mob = TexMobject(self.tex)
+        tex_mob.set_height(6)
+        path = tex_mob.family_members_with_points()[0]
+        path.set_fill(opacity=0)
+        path.set_stroke(WHITE, 1)
+        return path
+
+
+class FourierOfPiSymbol5(FourierOfPiSymbol):
+    CONFIG = {
+        "n_circles": 5,
+        "run_time": 10,
+    }
+
+
+class FourierOfTrebleClef(FourierOfPiSymbol):
+    CONFIG = {
+        "n_circles": 100,
+        "run_time": 10,
+        "start_drawn": True,
+    }
+
+    def get_path(self):
+        path = SVGMobject("TrebleClef")
+        path = path.family_members_with_points()[0]
+        path.set_height(7.5)
+        path.set_fill(opacity=0)
+        path.set_stroke(WHITE, 0)
+        return path
+
+
+class ExplainCircleAnimations(FourierCirclesScene):
+    CONFIG = {
+        # "n_circles": 100,
+        "n_circles": 20,
+        "center_point": 2 * DOWN,
+        "n_top_circles": 9,
+        # "slow_factor": 0.1,
+        "path_height": 3,
+    }
+
+    def construct(self):
+        self.add_path()
+        self.add_circles()
+        self.organize_circles_in_a_row()
+        self.show_frequencies()
+        self.show_examples_for_frequencies()
+        self.show_as_vectors()
+        self.show_vector_sum()
+        self.moons_of_moons_of_moons()
+        self.tweak_starting_vectors()
+
+    def add_path(self):
+        self.path = self.get_path()
+        self.add(self.path)
+
+    def add_circles(self):
+        coefs = self.get_coefficients_of_path(self.path)
+        self.circles = self.get_circles(coefficients=coefs)
+
+        self.add(self.circles)
+        self.drawn_path = self.get_drawn_path(self.circles)
+        self.add(self.drawn_path)
+
+        self.wait(8)
+
+    def organize_circles_in_a_row(self):
+        circles = self.circles
+        top_circles = circles[:self.n_top_circles].deepcopy()
+
+        center_trackers = VGroup()
+        for circle in top_circles:
+            tracker = VectorizedPoint(circle.center_func())
+            circle.center_func = tracker.get_location
+            center_trackers.add(tracker)
+            tracker.freq = circle.freq
+            tracker.circle = circle
+
+        center_trackers.submobjects.sort(
+            key=lambda m: m.freq
+        )
+        center_trackers.generate_target()
+        right_buff = 1.45
+        center_trackers.target.arrange(RIGHT, buff=right_buff)
+        center_trackers.target.to_edge(UP, buff=1.25)
+
+        self.add(top_circles)
+        self.play(
+            MoveToTarget(center_trackers),
+            run_time=2
+        )
+        self.wait(4)
+
+        self.top_circles = top_circles
+        self.center_trackers = center_trackers
+
+    def show_frequencies(self):
+        center_trackers = self.center_trackers
+
+        freq_numbers = VGroup()
+        for ct in center_trackers:
+            number = Integer(ct.freq)
+            number.next_to(ct, DOWN, buff=1)
+            freq_numbers.add(number)
+            ct.circle.number = number
+
+        ld, rd = [
+            TexMobject("\\dots")
+            for x in range(2)
+        ]
+        ld.next_to(freq_numbers, LEFT, MED_LARGE_BUFF)
+        rd.next_to(freq_numbers, RIGHT, MED_LARGE_BUFF)
+        freq_numbers.add_to_back(ld)
+        freq_numbers.add(rd)
+
+        freq_word = TextMobject("Frequencies")
+        freq_word.scale(1.5)
+        freq_word.set_color(YELLOW)
+        freq_word.next_to(freq_numbers, DOWN, MED_LARGE_BUFF)
+
+        self.play(
+            LaggedStartMap(
+                FadeInFromDown, freq_numbers
+            )
+        )
+        self.play(
+            Write(freq_word),
+            LaggedStartMap(
+                ShowCreationThenFadeAround, freq_numbers,
+            )
+        )
+        self.wait(2)
+
+    def show_examples_for_frequencies(self):
+        top_circles = self.top_circles
+        c1, c2, c3 = [
+            list(filter(
+                lambda c: c.freq == k,
+                top_circles
+            ))[0]
+            for k in (1, 2, 3)
+        ]
+
+        neg_circles = VGroup(*filter(
+            lambda c: c.freq < 0,
+            top_circles
+        ))
+
+        for c in [c1, c2, c3, *neg_circles]:
+            c.rect = SurroundingRectangle(c)
+
+        self.play(
+            ShowCreation(c2.rect),
+            WiggleOutThenIn(c2.number),
+        )
+        self.wait(2)
+        self.play(
+            ReplacementTransform(c2.rect, c1.rect),
+        )
+        self.play(FadeOut(c1.rect))
+        self.wait()
+        self.play(
+            ShowCreation(c3.rect),
+            WiggleOutThenIn(c3.number),
+        )
+        self.play(
+            FadeOut(c3.rect),
+        )
+        self.wait(2)
+        self.play(
+            LaggedStart(*[
+                ShowCreationThenFadeOut(c.rect)
+                for c in neg_circles
+            ])
+        )
+        self.wait(3)
+
+    def show_as_vectors(self):
+        top_circles = self.top_circles
+        top_vectors = self.get_rotating_vectors(top_circles)
+
+        self.play(
+            top_circles.set_stroke, {"width": 0.5},
+            FadeIn(top_vectors),
+        )
+        self.wait(3)
+
+        self.top_vectors = top_vectors
+
+    def show_vector_sum(self):
+        top_circles = self.top_circles
+        top_vectors = self.top_vectors
+
+        self.play(
+            FadeOut(self.path),
+            FadeOut(self.circles),
+        )
+
+    def moons_of_moons_of_moons(self):
+        pass
+
+    def tweak_starting_vectors(self):
+        pass
+
+    #
+    def get_path(self):
+        tex = TexMobject("f")
+        path = tex.family_members_with_points()[0]
+        path.set_stroke(WHITE, 1)
+        path.set_fill(opacity=0)
+        path.set_height(self.path_height)
+        path.move_to(self.center_point)
+        return path
+        # return Square().set_height(3)

active_projects/ode/part2/heat_equation.py

@@ -0,0 +1,6 @@
+from big_ol_pile_of_manim_imports import *
+
+
+class NewSceneName(Scene):
+    def construct(self):
+        pass

active_projects/ode/part2/staging.py

@@ -0,0 +1,22 @@
+from big_ol_pile_of_manim_imports import *
+
+
+class FourierSeriesIntro(Scene):
+    def construct(self):
+        title = TextMobject(
+            "Fourier ", "Series", ":",
+            " An origin story",
+            arg_separator="",
+        )
+        title.scale(2)
+        title.to_edge(UP)
+        image = ImageMobject("Joseph Fourier")
+        image.set_height(5)
+        image.next_to(title, DOWN, MED_LARGE_BUFF)
+        image.to_edge(LEFT)
+        name = TextMobject("Joseph", "Fourier")
+        name.next_to(image, DOWN)
+
+        self.add(title)
+        self.add(image)
+        self.add(name)

active_projects/ode/solve_pendulum_ode_sample_code.py

@@ -0,0 +1,63 @@
+import numpy as np
+
+# Physical constants
+g = 9.8
+L = 2
+mu = 0.1
+
+THETA_0 = np.pi / 3  # 60 degrees
+THETA_DOT_0 = 0  # No initial angular velocity
+
+# Definition of ODE
+def get_theta_double_dot(theta, theta_dot):
+    return -mu * theta_dot - (g / L) * np.sin(theta)
+
+
+# Solution to the differential equation
+def theta(t):
+    # Initialize changing values
+    theta = THETA_0
+    theta_dot = THETA_DOT_0
+    delta_t = 0.01  # Some time step
+    for time in np.arange(0, t, delta_t):
+        # Take many little time steps of size delta_t
+        # until the total time is the function's input
+        theta_double_dot = get_theta_double_dot(
+            theta, theta_dot
+        )
+        theta += theta_dot * delta_t
+        theta_dot += theta_double_dot * delta_t
+    return theta
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+

manimlib/animation/composition.py

@@ -151,8 +151,11 @@ class LaggedStartMap(LaggedStart):
                 args_list.append(arg_creator(submob))
             else:
                 args_list.append((submob,))
+        anim_kwargs = dict(kwargs)
+        if "lag_ratio" in anim_kwargs:
+            anim_kwargs.pop("lag_ratio")
         animations = [
-            AnimationClass(*args, **kwargs)
+            AnimationClass(*args, **anim_kwargs)
             for args in args_list
         ]
         super().__init__(*animations, **kwargs)

manimlib/for_3b1b_videos/common_scenes.py

@@ -102,7 +102,7 @@ class PatreonThanks(Scene):
         patreon_logo = PatreonLogo()
         patreon_logo.to_edge(UP)
 
-        patrons = list(map(TextMobject, self.specific_patrons))
+        patrons = list(map(TextMobject, self.specific_patronds))
         num_groups = float(len(patrons)) / self.max_patron_group_size
         proportion_range = np.linspace(0, 1, num_groups + 1)
         indices = (len(patrons) * proportion_range).astype('int')
@@ -213,7 +213,14 @@ class PatreonEndScreen(PatreonThanks, PiCreatureScene):
         underline.next_to(thanks, DOWN, SMALL_BUFF)
         thanks.add(underline)
 
-        patrons = VGroup(*list(map(TextMobject, self.specific_patrons)))
+        changed_patron_names = map(
+            self.modify_patron_name,
+            self.specific_patrons,
+        )
+        patrons = VGroup(*map(
+            TextMobject,
+            changed_patron_names,
+        ))
         patrons.scale(self.patron_scale_val)
         for patron in patrons:
             if patron.get_width() > self.max_patron_width:
@@ -252,6 +259,11 @@ class PatreonEndScreen(PatreonThanks, PiCreatureScene):
         self.add(columns, black_rect, line, thanks)
         self.wait(wait_time)
 
+    def modify_patron_name(self, name):
+        if name is "RedAgent14":
+            return "Brian Shepetofsky"
+        return name
+
 
 class LogoGenerationTemplate(MovingCameraScene):
     def setup(self):

manimlib/for_3b1b_videos/pi_creature_scene.py

@@ -174,6 +174,7 @@ class PiCreatureScene(Scene):
                 continue
             anims_with_pi_creature = [anim for anim in animations if pi_creature in anim.mobject.get_family()]
             for anim in anims_with_pi_creature:
+                continue  # TODO, this is broken
                 if isinstance(anim, Transform):
                     index = anim.mobject.get_family().index(pi_creature)
                     target_family = anim.target_mobject.get_family()

manimlib/mobject/changing.py

@@ -8,6 +8,9 @@ class AnimatedBoundary(VGroup):
         "colors": [BLUE_D, BLUE_B, BLUE_E, GREY_BROWN],
         "max_stroke_width": 3,
         "cycle_rate": 0.5,
+        "back_and_forth": True,
+        "draw_rate_func": smooth,
+        "fade_rate_func": smooth,
     }
 
     def __init__(self, vmobject, **kwargs):
@@ -22,9 +25,11 @@ class AnimatedBoundary(VGroup):
         ]
         self.add(*self.boundary_copies)
         self.total_time = 0
-        self.add_updater(lambda m, dt: self.update(dt))
+        self.add_updater(
+            lambda m, dt: self.update_boundary_copies(dt)
+        )
 
-    def update(self, dt):
+    def update_boundary_copies(self, dt):
         # Not actual time, but something which passes at
         # an altered rate to make the implementation below
         # cleaner
@@ -35,12 +40,14 @@ class AnimatedBoundary(VGroup):
         vmobject = self.vmobject
 
         index = int(time % len(colors))
-        alpha = smooth(time % 1)
+        alpha = time % 1
+        draw_alpha = self.draw_rate_func(alpha)
+        fade_alpha = self.fade_rate_func(alpha)
 
-        if int(time) % 2 == 0:
-            bounds = (0, alpha)
+        if self.back_and_forth and int(time) % 1 == 0:
+            bounds = (1 - draw_alpha, 1)
         else:
-            bounds = (1 - alpha, 1)
+            bounds = (0, draw_alpha)
         self.full_family_become_partial(growing, vmobject, *bounds)
         growing.set_stroke(colors[index], width=msw)
 
@@ -48,7 +55,7 @@ class AnimatedBoundary(VGroup):
             self.full_family_become_partial(fading, vmobject, 0, 1)
             fading.set_stroke(
                 color=colors[index - 1],
-                width=(1 - alpha) * msw
+                width=(1 - fade_alpha) * msw
             )
 
         self.total_time += dt

manimlib/mobject/coordinate_systems.py

@@ -82,7 +82,7 @@ class CoordinateSystem():
                 )[0],
                 target=x,
                 lower_bound=self.x_min,
-                uplper_bound=self.x_max,
+                upper_bound=self.x_max,
             )
             if alpha is not None:
                 return graph.point_from_proportion(alpha)

manimlib/mobject/mobject_update_utils.py

@@ -22,7 +22,7 @@ def always(method, *args, **kwargs):
 
 def f_always(method, *arg_generators, **kwargs):
     """
-    More functional version of always, where insetead
+    More functional version of always, where instead
     of taking in args, it takes in functions which ouput
     the relevant arguments.
     """
@@ -77,13 +77,12 @@ def turn_animation_into_updater(animation, cycle=False, **kwargs):
 
     def update(m, dt):
         run_time = animation.get_run_time()
-        alpha = np.clip(
-            animation.total_time / run_time,
-            0, 1,
-        )
+        time_ratio = animation.total_time / run_time
         if cycle:
-            animation.total_time = animation.total_time % run_time
-        elif alpha >= 1:
+            alpha = time_ratio % 1
+        else:
+            alpha = np.clip(time_ratio, 0, 1)
+            if alpha >= 1:
                 animation.finish()
                 m.remove_updater(update)
                 return

manimlib/mobject/number_line.py

@@ -95,9 +95,10 @@ class NumberLine(Line):
         )
 
     def get_tick_numbers(self):
+        u = -1 if self.include_tip else 1
         return np.arange(
             self.leftmost_tick,
-            self.x_max + self.tick_frequency / 2,
+            self.x_max + u * self.tick_frequency / 2,
             self.tick_frequency
         )
 

manimlib/mobject/svg/drawings.py

@@ -393,11 +393,13 @@ class ClockPassesTime(Animation):
             radians=hour_radians,
             **rot_kwargs
         )
+        self.hour_rotation.begin()
         self.minute_rotation = Rotating(
             clock.minute_hand,
             radians=12 * hour_radians,
             **rot_kwargs
         )
+        self.minute_rotation.begin()
         Animation.__init__(self, clock, **kwargs)
 
     def interpolate_mobject(self, alpha):

old_projects/div_curl.py

@@ -2817,18 +2817,16 @@ class ShowTwoPopulations(Scene):
         num_foxes = Integer(10)
         num_foxes.scale(self.count_word_scale_val)
         num_foxes.next_to(labels[0], RIGHT)
-        num_foxes.align_to(labels[0][1], DOWN)
+        num_foxes.align_to(labels[0][0][1], DOWN)
         num_rabbits = Integer(10)
         num_rabbits.scale(self.count_word_scale_val)
         num_rabbits.next_to(labels[1], RIGHT)
-        num_rabbits.align_to(labels[1][1], DOWN)
+        num_rabbits.align_to(labels[1][0][1], DOWN)
 
-        self.add(ContinualChangingDecimal(
-            num_foxes, lambda a: get_num_foxes()
-        ))
-        self.add(ContinualChangingDecimal(
-            num_rabbits, lambda a: get_num_rabbits()
-        ))
+        num_foxes.add_updater(lambda d: d.set_value(get_num_foxes()))
+        num_rabbits.add_updater(lambda d: d.set_value(get_num_rabbits()))
+
+        self.add(num_foxes, num_rabbits)
 
         for count in num_foxes, num_rabbits:
             self.add(Mobject.add_updater(
@@ -2853,13 +2851,13 @@ class ShowTwoPopulations(Scene):
             height=self.animal_height,
             fill_color=color,
         )
-        for submob in result.family_members_with_points():
-            if submob.is_subpath:
-                submob.is_subpath = False
-                submob.set_fill(
-                    interpolate_color(color, BLACK, 0.8),
-                    opacity=1
-                )
+        # for submob in result.family_members_with_points():
+            # if submob.is_subpath:
+            #     submob.is_subpath = False
+            #     submob.set_fill(
+            #         interpolate_color(color, BLACK, 0.8),
+            #         opacity=1
+            #     )
         x_shift, y_shift = [
             (2 * random.random() - 1) * max_val
             for max_val in [
@@ -3021,25 +3019,7 @@ class PhaseSpaceOfPopulationModel(ShowTwoPopulations, PiCreatureScene, MovingCam
         self.pop_sizes_updates = pop_sizes_updates
 
     def write_differential_equations(self):
-        variables = ["X", "YY"]
-        equations = TexMobject(
-            """
-                {dX \\over dt} =
-                X \\cdot (\\alpha - \\beta YY \\,) \\\\
-                \\quad \\\\
-                {dYY \\over dt} =
-                YY \\cdot (\\delta X - \\gamma)
-            """,
-            substrings_to_isolate=variables
-        )
-        animals = [self.get_rabbit(), self.get_fox().flip()]
-        for char, animal in zip(variables, animals):
-            for part in equations.get_parts_by_tex(char):
-                animal_copy = animal.copy()
-                animal_copy.set_height(0.5)
-                animal_copy.move_to(part, DL)
-                Transform(part, animal_copy).update(1)
-
+        equations = self.get_equations()
         equations.shift(2 * DOWN)
         rect = SurroundingRectangle(equations, color=YELLOW)
         rect.set_fill(BLACK, 0.8)
@@ -3183,6 +3163,28 @@ class PhaseSpaceOfPopulationModel(ShowTwoPopulations, PiCreatureScene, MovingCam
         )
         self.wait(self.flow_time)
 
+    #
+    def get_equations(self):
+        variables = ["X", "YY"]
+        equations = TexMobject(
+            """
+                {dX \\over dt} =
+                X \\cdot (\\alpha - \\beta YY \\,) \\\\
+                \\quad \\\\
+                {dYY \\over dt} =
+                YY \\cdot (\\delta X - \\gamma)
+            """,
+            substrings_to_isolate=variables
+        )
+        animals = [self.get_rabbit(), self.get_fox().flip()]
+        for char, animal in zip(variables, animals):
+            for part in equations.get_parts_by_tex(char):
+                animal_copy = animal.copy()
+                animal_copy.set_height(0.5)
+                animal_copy.move_to(part, DL)
+                part.become(animal_copy)
+        return equations
+
 
 class PhaseFlowWords(Scene):
     def construct(self):

stage_scenes.py

@@ -43,7 +43,7 @@ def stage_scenes(module_name):
     # }
     # TODO, fix this
     animation_dir = os.path.join(
-        VIDEO_DIR, "clacks_solution2", "1440p60"
+        VIDEO_DIR, "ode", "part1", "1440p60"
     )
     # 
     files = os.listdir(animation_dir)