From fdccfd51fcc45dc7b6b10e2c331835dca1f1f305 Mon Sep 17 00:00:00 2001
From: Grant Sanderson <grant@3blue1brown.com>
Date: Thu, 29 Dec 2022 19:43:12 -0800
Subject: [PATCH] Add TexAndNumbersExample

---
 example_scenes.py | 68 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/example_scenes.py b/example_scenes.py
index c1a2fa50..f005cecf 100644
--- a/example_scenes.py
+++ b/example_scenes.py
@@ -453,6 +453,74 @@ class GraphExample(Scene):
         self.wait()
 
 
+class TexAndNumbersExample(InteractiveScene):
+    def construct(self):
+        axes = Axes((-3, 3), (-3, 3), unit_size=1)
+        axes.to_edge(DOWN)
+        axes.add_coordinate_labels(font_size=16)
+        circle = Circle(radius=2)
+        circle.set_stroke(YELLOW, 3)
+        circle.move_to(axes.get_origin())
+        self.add(axes, circle)
+
+        # When numbers show up in tex, they can be readily
+        # replaced with DecimalMobjects so that methods like
+        # get_value and set_value can be called on them, and
+        # animations like ChangeDecimalToValue can be called
+        # on them.
+        tex = Tex("x^2 + y^2 = 4.00")
+        tex.next_to(axes, UP, buff=0.5)
+        value = tex.make_number_changable("4.00")
+
+
+        # This will tie the right hand side of our equation to
+        # the square of the radius of the circle
+        value.add_updater(lambda v: v.set_value(circle.get_radius()**2))
+        self.add(tex)
+
+        text = Text("""
+            You can manipulate numbers
+            in Tex mobjects
+        """, font_size=30)
+        text.next_to(tex, RIGHT, buff=1.5)
+        arrow = Arrow(text, tex)
+        self.add(text, arrow)
+
+        self.play(
+            circle.animate.set_height(2.0),
+            run_time=4,
+            rate_func=there_and_back,
+        )
+
+        # By default, tex.make_number_changable replaces the first occurance
+        # of the number,but by passing replace_all=True it replaces all and
+        # returns a group of the results
+        exponents = tex.make_number_changable("2", replace_all=True)
+        self.play(
+            LaggedStartMap(
+                FlashAround, exponents,
+                lag_ratio=0.2, buff=0.1, color=RED
+            ),
+            exponents.animate.set_color(RED)
+        )
+
+        def func(x, y):
+            # Switch from manim coords to axes coords
+            xa, ya = axes.point_to_coords(np.array([x, y, 0]))
+            return xa**4 + ya**4 - 4
+
+        new_curve = ImplicitFunction(func)
+        new_curve.match_style(circle)
+        circle.rotate(angle_of_vector(new_curve.get_start()))  # Align
+        value.clear_updaters()
+
+        self.play(
+            *(ChangeDecimalToValue(exp, 4) for exp in exponents),
+            ReplacementTransform(circle.copy(), new_curve),
+            circle.animate.set_stroke(width=1, opacity=0.5),
+        )
+
+
 class SurfaceExample(Scene):
     default_camera_config = dict(samples=4)