Rework example for :class:~.Variable

[UraniumCronorum]

Changelog / Overview

Motivation

Pull request for this hackathon submission.

(My Discord tag: UraniumCronorum#9747)

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Documentation Reference

Testing Status

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[PhotonSpheres]

Hey there, thank you for your contribution!
Unfortunately, I don't think this example fits well: Since you interpolate linearly between the beginning numbers and their respective end numbers, there will be wrong equations on-screen during the animation, see the screenshot below.
I guess one fix would be to calculate the square number for each frame.

[PhotonSpheres]

If you don't mind a little more input, I can suggest the following changes to your example:

class VariableExample(Scene):
    def construct(self):
        x = 0
        x_sqr = x**2
        x_display = Variable(x, "x", num_decimal_places=3)
        sqr_display = Variable(x_sqr, "x^2", num_decimal_places=3).next_to(x_display,DOWN)
        Group(x_display, sqr_display).center()
        self.play(
            Write(x_display),
            Write(sqr_display)
        )
        x_tracker = x_display.tracker
        sqr_tracker = sqr_display.tracker
        x = 5.6
        x_sqr = x**2
        self.play(
            x_tracker.animate(rate_func=linear).set_value(x),
            sqr_tracker.animate(rate_func=lambda x: x**2).set_value(x_sqr),
        )
        self.wait()

VariableExample.mp4

[UraniumCronorum]

Hi, thanks for the feedback.

I tried running the code you suggested and it seems to work fine, but when I change the initial value of x to something other than 0, the results start to get out of sync again. I'm trying to figure out how to fix this, but I haven't made much progress yet.

I also tried your suggestion about calculating the values for each frame, and this seems to work:

class VariableExample(Scene):
    def construct(self):
        start = 2.0

        x_var = Variable(start, 'x', num_decimal_places=3)
        sqr_var = Variable(start**2, 'x^2',
                           num_decimal_places=3).next_to(x_var, DOWN)
        self.add(x_var, sqr_var)

        x_var.tracker.add_updater(lambda m, dt: m.set_value(m.get_value()+dt))
        sqr_var.tracker.add_updater(lambda m:
                                    m.set_value(x_var.tracker.get_value()**2))
        self.add(x_var.tracker)
        self.add(sqr_var.tracker)

        self.wait(3)

[PhotonSpheres]

I tried running the code you suggested and it seems to work fine, but when I change the initial value of x to something other than 0, the results start to get out of sync again. I'm trying to figure out how to fix this, but I haven't made much progress yet.

This is due to how rate_func. I don't know how easy it would be to generalize my suggestion to other start values than 0.

I also tried your suggestion about calculating the values for each frame, and this seems to work:

I really like your example, just adding the tracker to the scene seems a bit weird to me. I think, building up on your idea, this might be a bit cleaner

class VariableExample(Scene):
    def construct(self):
        start = 2.0

        x_var = Variable(start, 'x', num_decimal_places=3)
        sqr_var = Variable(start**2, 'x^2', num_decimal_places=3)
        Group(x_var, sqr_var).arrange(DOWN)

        sqr_var.add_updater(lambda v: v.tracker.set_value(x_var.tracker.get_value()**2))

        self.add(x_var, sqr_var)
        self.play(x_var.tracker.animate.set_value(5), run_time=2, rate_func=linear)
        self.wait(0.1)

What do you think?

[behackl]

I like the latest suggestion by @PhotonSpheres, +1 for reworking the example from this PR in that direction.

Also, instead of removing the current example, I suggest to keep the current one and add this as an additional example.

[PhotonSpheres]

LGTM! Cheers again

[behackl]

LGTM! Thanks for your contribution!