Further in chapter 2 of eola

animation/transform.py

@@ -93,9 +93,15 @@ class ApplyMethod(Transform):
         )
 
 class FadeOut(ApplyMethod):
+    CONFIG = {
+        "remover" : True, 
+    }
     def __init__(self, mobject, **kwargs):
         ApplyMethod.__init__(self, mobject.fade, 1, **kwargs)
 
+    def cleanup(self):
+        self.update(0)
+
 class FadeIn(Transform):
     def __init__(self, mobject, **kwargs):
         target = mobject.copy()

eola/chapter2.py

@@ -31,7 +31,6 @@ class OpeningQuote(Scene):
         words.to_edge(UP)    
         for mob in words.submobjects[49:49+18]:
             mob.highlight(GREEN)
-        words.show()
         author = TextMobject("-Angus K. Rodgers")
         author.highlight(YELLOW)
         author.next_to(words, DOWN, buff = 0.5)
@@ -53,17 +52,21 @@ class CoordinatesWereFamiliar(TeacherStudentsScene):
 
 
 class CoordinatesAsScalars(VectorScene):
+    CONFIG = {
+        "vector_coords" : [3, -2]
+    }
+
     def construct(self):
         self.axes = self.add_axes()
-        vector = self.add_vector([3, -2])
+        vector = self.add_vector(self.vector_coords)
         array, x_line, y_line = self.vector_to_coords(vector)
         self.add(array)
         self.dither()
-        new_array = self.general_idea_of_scalars(array)
+        new_array = self.general_idea_of_scalars(array, vector)
         self.scale_basis_vectors(new_array)
         self.show_symbolic_sum(new_array, vector)
 
-    def general_idea_of_scalars(self, array):
+    def general_idea_of_scalars(self, array, vector):
         starting_mobjects = self.get_mobjects()
 
         title = TextMobject("Think of each coordinate as a scalar")
@@ -76,14 +79,23 @@ class CoordinatesAsScalars(VectorScene):
         new_y.move_to(3*RIGHT+2*UP)
 
         i_hat, j_hat = self.get_basis_vectors()
-        new_i_hat = Vector(3*i_hat.get_end(), color = X_COLOR)
+        new_i_hat = Vector(
-        new_j_hat = Vector(-2*j_hat.get_end(), color = Y_COLOR)
+            self.vector_coords[0]*i_hat.get_end(), 
+            color = X_COLOR
+        )
+        new_j_hat = Vector(
+            self.vector_coords[1]*j_hat.get_end(), 
+            color = Y_COLOR
+        )
         VMobject(i_hat, new_i_hat).shift(3*LEFT)
         VMobject(j_hat, new_j_hat).shift(3*RIGHT)
 
         new_array = Matrix([new_x.copy(), new_y.copy()])
-        new_array.replace(array)
+        new_array.scale(0.5)
-        new_array.shift(0.5*DOWN)
+        new_array.shift(
+            -new_array.get_boundary_point(-vector.get_end()) + \
+            1.1*vector.get_end()
+        )
 
         self.remove(*starting_mobjects)
         self.play(
@@ -95,15 +107,16 @@ class CoordinatesAsScalars(VectorScene):
         self.dither()
         self.play(
             Transform(i_hat, new_i_hat),
-            Transform(j_hat, new_j_hat)
+            Transform(j_hat, new_j_hat),
+            run_time = 3
         )
         self.dither()
         starting_mobjects.remove(array)
+
+        new_x, new_y = new_array.get_mob_matrix().flatten()
         self.play(
-            Transform(
+            Transform(x, new_x),
-                VMobject(x, y),
+            Transform(y, new_y),
-                VMobject(*new_array.get_mob_matrix().flatten())
-            ),
             FadeOut(i_hat),
             FadeOut(j_hat),
             Write(new_array.get_brackets()),
@@ -117,8 +130,6 @@ class CoordinatesAsScalars(VectorScene):
     def scale_basis_vectors(self, new_array):
         self.play(ApplyMethod(self.axes.highlight, GREY))
         i_hat, j_hat = self.get_basis_vectors()
-        for mob in i_hat, j_hat:
-            mob.set_stroke(width = 6)
         self.add_vector(i_hat)
         i_hat_label = self.label_vector(
             i_hat, "\\hat{\\imath}", 
@@ -131,19 +142,20 @@ class CoordinatesAsScalars(VectorScene):
             color = Y_COLOR, 
             label_scale_val = 1
         )
+        self.dither()
 
         x, y = new_array.get_mob_matrix().flatten()
         for coord, v, label, factor, shift_right in [
-            (x, i_hat, i_hat_label, 3, False), 
+            (x, i_hat, i_hat_label, self.vector_coords[0], False), 
-            (y, j_hat, j_hat_label, -2, True)
+            (y, j_hat, j_hat_label, self.vector_coords[1], True)
             ]:
-            faded_v = v.copy().fade(0.5)
+            faded_v = v.copy().fade(0.7)
             scaled_v = Vector(factor*v.get_end(), color = v.get_color())
 
             scaled_label = VMobject(coord.copy(), label.copy())
             scaled_label.arrange_submobjects(RIGHT, buff = 0.1)
             scaled_label.move_to(label, DOWN+RIGHT)
-            scaled_label.shift(scaled_v.get_center()-v.get_center())
+            scaled_label.shift((scaled_v.get_end()-v.get_end())/2)
             coord_copy = coord.copy()
             self.play(
                 Transform(v.copy(), faded_v),
@@ -153,15 +165,20 @@ class CoordinatesAsScalars(VectorScene):
             self.dither()
             if shift_right:
                 group = VMobject(v, coord_copy, label)
-                self.play(ApplyMethod(group.shift, 3*RIGHT))
+                self.play(ApplyMethod(
+                    group.shift, self.vector_coords[0]*RIGHT
+                ))
         self.dither()
 
 
     def show_symbolic_sum(self, new_array, vector):
         new_mob = TexMobject([
-            "3\\hat{\\imath}", "+", "(-2)\\hat{\\jmath}"
+            "(%d)\\hat{\\imath}"%self.vector_coords[0], 
+            "+", 
+            "(%d)\\hat{\\jmath}"%self.vector_coords[1]
         ])
-        new_mob.shift(vector.get_end()-new_mob.get_corner(UP+LEFT))
+        new_mob.move_to(new_array)
+        new_mob.shift_onto_screen()
         i_hat, plus, j_hat = new_mob.split()
         i_hat.highlight(X_COLOR)
         j_hat.highlight(Y_COLOR)
@@ -171,13 +188,30 @@ class CoordinatesAsScalars(VectorScene):
         
 
 
-
+class CoordinatesAsScalarsExample2(CoordinatesAsScalars):
-
+    CONFIG = {
-
+        "vector_coords" : [-5, 2]
-
+    }
-
+
-
+    def construct(self):
-
+        self.add_axes()
+        basis_vectors = self.get_basis_vectors()
+        labels = self.get_basis_vector_labels()
+        self.add(*basis_vectors)
+        self.add(*labels)
+        text = TextMobject("""
+            $\\hat{\\imath}$ and $\\hat{\\jmath}$ 
+            are the ``basis vectors'' \\\\
+            of the $xy$ coordinate system
+        """)
+        text.scale_to_fit_width(SPACE_WIDTH-1)
+        text.to_corner(UP+RIGHT)
+        VMobject(*text.split()[:2]).highlight(X_COLOR)
+        VMobject(*text.split()[5:7]).highlight(Y_COLOR)
+        self.play(Write(text))
+        self.dither(2)
+        self.remove(*basis_vectors + labels)
+        CoordinatesAsScalars.construct(self)
 
 
 

eola/two_d_space.py

@@ -110,6 +110,9 @@ class LinearTransformationScene(Scene):
 
 
 class VectorScene(Scene):
+    CONFIG = {
+        "basis_vector_stroke_width" : 6
+    }
     def add_plane(self, animate = False, **kwargs):
         plane = NumberPlane(**kwargs)
         if animate:
@@ -133,13 +136,35 @@ class VectorScene(Scene):
         return vector
 
     def get_basis_vectors(self):
-        i_hat = Vector([1, 0], color = X_COLOR)
+        return [
-        j_hat = Vector([0, 1], color = Y_COLOR)
+            Vector(
-        return i_hat, j_hat
+                vect, color = color, 
+                stroke_width = self.basis_vector_stroke_width
+            )
+            for vect, color in [
+                ([1, 0], X_COLOR), 
+                ([0, 1], Y_COLOR)
+            ]
+        ]
+
+    def get_basis_vector_labels(self, animate = False, **kwargs):
+        i_hat, j_hat = self.get_basis_vectors()
+        return [
+            self.label_vector(
+                vect, label, color = color, 
+                animate = animate, 
+                label_scale_val = 1,
+                **kwargs
+            )
+            for vect, label , color in [
+                (i_hat, "\\hat{\\imath}", X_COLOR),
+                (j_hat, "\\hat{\\jmath}", Y_COLOR),
+            ]
+        ]
 
     def label_vector(self, vector, label, animate = True, 
                      direction = "left", rotate = False,
-                     color = WHITE, add_to_vector = True,
+                     color = WHITE, add_to_vector = False,
                      buff_factor = 2, 
                      label_scale_val = VECTOR_LABEL_SCALE_VAL):
         if len(label) == 1:
@@ -155,10 +180,10 @@ class VectorScene(Scene):
             rot_angle = -np.pi/2
         else:
             rot_angle = np.pi/2
-        label.shift(-buff_factor*label.get_critical_point(
+        boundary_dir = -np.round(rotate_vector(vector_vect, rot_angle))
-            rotate_vector(vector_vect, rot_angle)
+        boundary_point = label.get_critical_point(boundary_dir)
-        ))
+        label.shift(buff_factor*boundary_point)
-        label.shift(vector_vect/2)
+        label.shift(vector_vect/2.)
 
         if add_to_vector:
             vector.add(label)
@@ -202,8 +227,9 @@ class VectorScene(Scene):
             ),
             FadeOut(array.get_brackets())
         )
+        y_coord, brackets = self.get_mobjects_from_last_animation()
         self.play(ShowCreation(y_line))
-        self.play(ShowCreation(arrow, submobject_mode = "one_at_a_time"))
+        self.play(ShowCreation(arrow))
         self.dither()
         if cleanup:
             self.clear()
@@ -253,8 +279,8 @@ class VectorScene(Scene):
         )
         self.dither()
 
-        self.remove(x_coord_start, y_coord_start)
+        self.remove(x_coord_start, y_coord_start, brackets)
-        self.add(x_coord, y_coord)
+        self.add(array)
         if cleanup:
             self.clear()
             self.add(*starting_mobjects)