Manim:why is my graph plotted in half the animation time?

Question

I have this simple script, where I would like the ValueTracker (displayed as a number on the right) to evolve at the same speed with the graph. Instead the graph plotting finishes in 5 seconds. Do you know why and how to fix it?

from manim import *


class TrackerExample(Scene):

    def sin(self,x):
        f = 1 / 50
        return np.sin(x * 2 * math.pi * f) / 2 + 0.5

    def construct(self):

        axes= Axes(x_range=[0, 749, 100],
                            y_range=[0, 4, 2],
                            axis_config={"include_numbers": True, "font_size": 24},
                            x_axis_config={},
                            x_length=4,
                            y_length=3
                            ).move_to(LEFT * 2)



        self.play(Write(axes, lag_ratio=0.01, run_time=1))


        tracker = ValueTracker(0)


        sin_graph = axes.plot(lambda x: self.sin(x), color=BLUE)


        numbers = DecimalNumber(0).move_to(2*RIGHT)


        numbers.add_updater(lambda m: m.set_value(int(tracker.get_value())))


        self.add(numbers)


        self.play(tracker.animate.set_value(749), Write(sin_graph), run_time=10,
                  rate_func=linear)

example = TrackerExample()
example.construct()

I am using the community version of manim, 0.16.0.post0

Answer 1

This is due to your choice of Animation: Write draws, in the first 50% of the animation run time, the stroke of the mobject and then fills it in the remaining 50% of the run time. Replace Write with Create, and it will look as expected.

And by the way, if you want to render your scene directly from the script, use the render method, not construct:

example = TrackerExample()
example.render()