Variable#

Qualified name: manim.mobject.text.numbers.Variable

class Variable(var, label, var_type=<class 'manim.mobject.text.numbers.DecimalNumber'>, num_decimal_places=2, **kwargs)[source]#

Bases: VMobject

A class for displaying text that shows “label = value” with the value continuously updated from a ValueTracker.

Parameters

var (float) – The initial value you need to keep track of and display.
label (str | Tex | MathTex | Text | SingleStringMathTex) – The label for your variable. Raw strings are convertex to MathTex objects.
var_type (DecimalNumber | Integer) – The class used for displaying the number. Defaults to DecimalNumber.
num_decimal_places (int) – The number of decimal places to display in your variable. Defaults to 2. If var_type is an Integer, this parameter is ignored.
kwargs – Other arguments to be passed to ~.Mobject.

label#

The label for your variable, for example x = ....

Type: Union[str, Tex, MathTex, Text, SingleStringMathTex]

tracker#

Useful in updating the value of your variable on-screen.

Type: ValueTracker

value#

The tex for the value of your variable.

Type: Union[DecimalNumber, Integer]

Examples

Normal usage:

# DecimalNumber type
var = 0.5
on_screen_var = Variable(var, Text("var"), num_decimal_places=3)
# Integer type
int_var = 0
on_screen_int_var = Variable(int_var, Text("int_var"), var_type=Integer)
# Using math mode for the label
on_screen_int_var = Variable(int_var, "{a}_{i}", var_type=Integer)

Example: VariablesWithValueTracker ¶

from manim import *

class VariablesWithValueTracker(Scene):
    def construct(self):
        var = 0.5
        on_screen_var = Variable(var, Text("var"), num_decimal_places=3)

        # You can also change the colours for the label and value
        on_screen_var.label.set_color(RED)
        on_screen_var.value.set_color(GREEN)

        self.play(Write(on_screen_var))
        # The above line will just display the variable with
        # its initial value on the screen. If you also wish to
        # update it, you can do so by accessing the `tracker` attribute
        self.wait()
        var_tracker = on_screen_var.tracker
        var = 10.5
        self.play(var_tracker.animate.set_value(var))
        self.wait()

        int_var = 0
        on_screen_int_var = Variable(
            int_var, Text("int_var"), var_type=Integer
        ).next_to(on_screen_var, DOWN)
        on_screen_int_var.label.set_color(RED)
        on_screen_int_var.value.set_color(GREEN)

        self.play(Write(on_screen_int_var))
        self.wait()
        var_tracker = on_screen_int_var.tracker
        var = 10.5
        self.play(var_tracker.animate.set_value(var))
        self.wait()

        # If you wish to have a somewhat more complicated label for your
        # variable with subscripts, superscripts, etc. the default class
        # for the label is MathTex
        subscript_label_var = 10
        on_screen_subscript_var = Variable(subscript_label_var, "{a}_{i}").next_to(
            on_screen_int_var, DOWN
        )
        self.play(Write(on_screen_subscript_var))
        self.wait()

Example: VariableExample ¶

from manim import *

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)

Methods

Attributes

`animate`	Used to animate the application of any method of `self`.
`animation_overrides`
`color`
`depth`	The depth of the mobject.
`fill_color`	If there are multiple colors (for gradient) this returns the first one
`height`	The height of the mobject.
`n_points_per_curve`
`sheen_factor`
`stroke_color`
`width`	The width of the mobject.