graph_scene.py

import itertools as it

from manimlib.animation.creation import Write, DrawBorderThenFill, ShowCreation
from manimlib.animation.transform import Transform
from manimlib.animation.update import UpdateFromAlphaFunc
from manimlib.constants import *
from manimlib.mobject.functions import ParametricFunction
from manimlib.mobject.geometry import Line
from manimlib.mobject.geometry import Rectangle
from manimlib.mobject.geometry import RegularPolygon
from manimlib.mobject.number_line import NumberLine
from manimlib.mobject.svg.tex_mobject import TexMobject
from manimlib.mobject.svg.tex_mobject import TextMobject
from manimlib.mobject.types.vectorized_mobject import VGroup
from manimlib.mobject.types.vectorized_mobject import VectorizedPoint
from manimlib.scene.scene import Scene
from manimlib.utils.bezier import interpolate
from manimlib.utils.color import color_gradient
from manimlib.utils.color import invert_color
from manimlib.utils.space_ops import angle_of_vector

# TODO, this should probably reimplemented entirely, especially so as to
# better reuse code from mobject/coordinate_systems.
# Also, I really dislike how the configuration is set up, this
# is way too messy to work with.


class GraphScene(Scene):
    CONFIG = {
        "x_min": -1,
        "x_max": 10,
        "x_axis_width": 9,
        "x_tick_frequency": 1,
        "x_leftmost_tick": None,  # Change if different from x_min
        "x_labeled_nums": None,
        "x_axis_label": "$x$",
        "y_min": -1,
        "y_max": 10,
        "y_axis_height": 6,
        "y_tick_frequency": 1,
        "y_bottom_tick": None,  # Change if different from y_min
        "y_labeled_nums": None,
        "y_axis_label": "$y$",
        "axes_color": GREY,
        "graph_origin": 2.5 * DOWN + 4 * LEFT,
        "exclude_zero_label": True,
        "default_graph_colors": [BLUE, GREEN, YELLOW],
        "default_derivative_color": GREEN,
        "default_input_color": YELLOW,
        "default_riemann_start_color": BLUE,
        "default_riemann_end_color": GREEN,
        "area_opacity": 0.8,
        "num_rects": 50,
    }

    def setup(self):
        """
        This method is used internally by Manim
        to set up the scene for proper use.
        """
        self.default_graph_colors_cycle = it.cycle(self.default_graph_colors)

        self.left_T_label = VGroup()
        self.left_v_line = VGroup()
        self.right_T_label = VGroup()
        self.right_v_line = VGroup()

    def setup_axes(self, animate=False):
        """
        This method sets up the axes of the graph.

        Parameters
        ----------
        animate (bool=False)
            Whether or not to animate the setting up of the Axes.
        """
        # TODO, once eoc is done, refactor this to be less redundant.
        x_num_range = float(self.x_max - self.x_min)
        self.space_unit_to_x = self.x_axis_width / x_num_range
        if self.x_labeled_nums is None:
            self.x_labeled_nums = []
        if self.x_leftmost_tick is None:
            self.x_leftmost_tick = self.x_min
        x_axis = NumberLine(
            x_min=self.x_min,
            x_max=self.x_max,
            unit_size=self.space_unit_to_x,
            tick_frequency=self.x_tick_frequency,
            leftmost_tick=self.x_leftmost_tick,
            numbers_with_elongated_ticks=self.x_labeled_nums,
            color=self.axes_color
        )
        x_axis.shift(self.graph_origin - x_axis.number_to_point(0))
        if len(self.x_labeled_nums) > 0:
            if self.exclude_zero_label:
                self.x_labeled_nums = [x for x in self.x_labeled_nums if x != 0]
            x_axis.add_numbers(*self.x_labeled_nums)
        if self.x_axis_label:
            x_label = TextMobject(self.x_axis_label)
            x_label.next_to(
                x_axis.get_tick_marks(), UP + RIGHT,
                buff=SMALL_BUFF
            )
            x_label.shift_onto_screen()
            x_axis.add(x_label)
            self.x_axis_label_mob = x_label

        y_num_range = float(self.y_max - self.y_min)
        self.space_unit_to_y = self.y_axis_height / y_num_range

        if self.y_labeled_nums is None:
            self.y_labeled_nums = []
        if self.y_bottom_tick is None:
            self.y_bottom_tick = self.y_min
        y_axis = NumberLine(
            x_min=self.y_min,
            x_max=self.y_max,
            unit_size=self.space_unit_to_y,
            tick_frequency=self.y_tick_frequency,
            leftmost_tick=self.y_bottom_tick,
            numbers_with_elongated_ticks=self.y_labeled_nums,
            color=self.axes_color,
            line_to_number_vect=LEFT,
            label_direction=LEFT,
        )
        y_axis.shift(self.graph_origin - y_axis.number_to_point(0))
        y_axis.rotate(np.pi / 2, about_point=y_axis.number_to_point(0))
        if len(self.y_labeled_nums) > 0:
            if self.exclude_zero_label:
                self.y_labeled_nums = [y for y in self.y_labeled_nums if y != 0]
            y_axis.add_numbers(*self.y_labeled_nums)
        if self.y_axis_label:
            y_label = TextMobject(self.y_axis_label)
            y_label.next_to(
                y_axis.get_corner(UP + RIGHT), UP + RIGHT,
                buff=SMALL_BUFF
            )
            y_label.shift_onto_screen()
            y_axis.add(y_label)
            self.y_axis_label_mob = y_label

        if animate:
            self.play(Write(VGroup(x_axis, y_axis)))
        else:
            self.add(x_axis, y_axis)
        self.x_axis, self.y_axis = self.axes = VGroup(x_axis, y_axis)
        self.default_graph_colors = it.cycle(self.default_graph_colors)

    def coords_to_point(self, x, y):
        """
        The graph is smaller than the scene.
        Because of this, coordinates in the scene don't map
        to coordinates on the graph.
        This method returns a scaled coordinate for the graph,
        given cartesian coordinates that correspond to the scene..

        Parameters
        ----------
        x : (int,float)
            The x value

        y : (int,float)
            The y value
        
        Returns
        -------
        np.ndarray
            The array of the coordinates.
        """
        assert(hasattr(self, "x_axis") and hasattr(self, "y_axis"))
        result = self.x_axis.number_to_point(x)[0] * RIGHT
        result += self.y_axis.number_to_point(y)[1] * UP
        return result

    def point_to_coords(self, point):
        """
        The scene is smaller than the graph.

        Because of this, coordinates in the graph don't map
        to coordinates on the scene.

        This method returns a scaled coordinate for the scene,
        given coordinates that correspond to the graph.

        Parameters
        ----------
        point (np.ndarray)
            The point on the graph.
        
        Returns
        -------
        tuple
            The coordinates on the scene.
        """
        return (self.x_axis.point_to_number(point),
                self.y_axis.point_to_number(point))

    def get_graph(
        self, func,
        color=None,
        x_min=None,
        x_max=None,
        **kwargs
    ):
        """
        This method gets a curve to plot on the graph.

        Parameters
        ----------
        func : function
            The function to plot. It's return value should be
            the y-coordinate for a given x-coordinate
        
        color : str
            The string of the RGB color of the curve. in Hexadecimal representation.
        
        x_min : (Union[int,float])
            The lower x_value from which to plot the curve.
        
        x_max : (Union[int,float])
            The higher x_value until which to plot the curve.
        
        **kwargs:
            Any valid keyword arguments of ParametricFunction.

        Return
        ------
        ParametricFunction
            The Parametric Curve for the function passed.

        """
        if color is None:
            color = next(self.default_graph_colors_cycle)
        if x_min is None:
            x_min = self.x_min
        if x_max is None:
            x_max = self.x_max

        def parameterized_function(alpha):
            x = interpolate(x_min, x_max, alpha)
            y = func(x)
            if not np.isfinite(y):
                y = self.y_max
            return self.coords_to_point(x, y)

        graph = ParametricFunction(
            parameterized_function,
            color=color,
            **kwargs
        )
        graph.underlying_function = func
        return graph

    def input_to_graph_point(self, x, graph):
        """
        This method returns a coordinate on the curve
        given an x_value and a the graoh-curve for which
        the corresponding y value should be found.

        Parameters
        ----------
        x (Union[int, float])
            The x value for which to find the y value.
        
        graph ParametricFunction
            The ParametricFunction object on which
            the x and y value lie.
        
        Returns
        -------
        numpy.nparray
            The array of the coordinates on the graph.
        """
        return self.coords_to_point(x, graph.underlying_function(x))

    def angle_of_tangent(self, x, graph, dx=0.01):
        """
        Returns the angle to the x axis of the tangent
        to the plotted curve at a particular x-value.

        Parameters
        ----------
        x (Union[int, float])
            The x value at which the tangent must touch the curve.
        
        graph ParametricFunction
            The ParametricFunction for which to calculate the tangent.
        
        dx (Union(float, int =0.01))
            The small change in x with which a small change in y
            will be compared in order to obtain the tangent.
        
        Returns
        -------
        float
            The angle of the tangent with the x axis.
        """
        vect = self.input_to_graph_point(
            x + dx, graph) - self.input_to_graph_point(x, graph)
        return angle_of_vector(vect)

    def slope_of_tangent(self, *args, **kwargs):
        """
        Returns the slople of the tangent to the plotted curve 
        at a particular x-value.

        Parameters
        ----------
        x (Union[int, float])
            The x value at which the tangent must touch the curve.
        
        graph ParametricFunction
            The ParametricFunction for which to calculate the tangent.
        
        dx (Union(float, int =0.01))
            The small change in x with which a small change in y
            will be compared in order to obtain the tangent.
        
        Returns
        -------
        float
            The slope of the tangent with the x axis.
        """
        return np.tan(self.angle_of_tangent(*args, **kwargs))

    def get_derivative_graph(self, graph, dx=0.01, **kwargs):
        """
        Returns the curve of the derivative of the passed
        graph.

        Parameters
        ----------
        graph (ParametricFunction)
            The graph for which the derivative must be found.
        
        dx (Union(float, int =0.01))
            The small change in x with which a small change in y
            will be compared in order to obtain the derivative.
        
        **kwargs
            Any valid keyword argument of ParametricFunction
        
        Returns
        -------
        ParametricFuncion
            The curve of the derivative.
        """
        if "color" not in kwargs:
            kwargs["color"] = self.default_derivative_color

        def deriv(x):
            return self.slope_of_tangent(x, graph, dx) / self.space_unit_to_y
        return self.get_graph(deriv, **kwargs)

    def get_graph_label(
        self,
        graph,
        label="f(x)",
        x_val=None,
        direction=RIGHT,
        buff=MED_SMALL_BUFF,
        color=None,
    ):
        """
        This method returns a properly positioned label for the passed graph,
        styled with the passed parameters.

        Parameters
        ----------
        graph : ParametricFunction
            The curve of the function plotted.

        label : str = "f(x)"
            The label for the function's curve.

        x_val : Union[float, int]
            The x_value with which the label should be aligned.

        direction : Union[np.ndarray,list,tuple]=RIGHT
            The position, relative to the curve that the label will be at.
            e.g LEFT, RIGHT

        buff : Union[float, int]
            The buffer space between the curve and the label

        color : str
            The color of the label.
        
        Returns
        -------
        TexMobject
            The LaTeX of the passed 'label' parameter

        """
        label = TexMobject(label)
        color = color or graph.get_color()
        label.set_color(color)
        if x_val is None:
            # Search from right to left
            for x in np.linspace(self.x_max, self.x_min, 100):
                point = self.input_to_graph_point(x, graph)
                if point[1] < FRAME_Y_RADIUS:
                    break
            x_val = x
        label.next_to(
            self.input_to_graph_point(x_val, graph),
            direction,
            buff=buff
        )
        label.shift_onto_screen()
        return label

    def get_riemann_rectangles(
        self,
        graph,
        x_min=None,
        x_max=None,
        dx=0.1,
        input_sample_type="left",
        stroke_width=1,
        stroke_color=BLACK,
        fill_opacity=1,
        start_color=None,
        end_color=None,
        show_signed_area=True,
        width_scale_factor=1.001
    ):
        """
        This method returns the VGroup() of the Riemann Rectangles for
        a particular curve.

        Parameters
        ----------
        graph (ParametricFunction)
            The graph whose area needs to be approximated
            by the Riemann Rectangles.
        
        x_min Union[int,float]
            The lower bound from which to start adding rectangles
        
        x_max Union[int,float]
            The upper bound where the rectangles stop.
        
        dx Union[int,float]
            The smallest change in x-values that is 
            considered significant.
        
        input_sample_type str
            Can be any of "left", "right" or "center
        
        stroke_width : Union[int, float]
            The stroke_width of the border of the rectangles.
        
        stroke_color : str
            The string of hex colour of the rectangle's border.

        fill_opacity Union[int, float]
            The opacity of the rectangles.

        start_color : str,
            The hex starting colour for the rectangles,
            this will, if end_color is a different colour,
            make a nice gradient.
        
        end_color : str,
            The hex ending colour for the rectangles,
            this will, if start_color is a different colour,
            make a nice gradient.
        
        show_signed_area : bool (True)
            Whether or not to indicate -ve area if curve dips below
            x-axis.
        
        width_scale_factor : Union[int, float]
            How much the width of the rectangles are scaled by when transforming.
        
        Returns
        -------
        VGroup
            A VGroup containing the Riemann Rectangles.

        """
        x_min = x_min if x_min is not None else self.x_min
        x_max = x_max if x_max is not None else self.x_max
        if start_color is None:
            start_color = self.default_riemann_start_color
        if end_color is None:
            end_color = self.default_riemann_end_color
        rectangles = VGroup()
        x_range = np.arange(x_min, x_max, dx)
        colors = color_gradient([start_color, end_color], len(x_range))
        for x, color in zip(x_range, colors):
            if input_sample_type == "left":
                sample_input = x
            elif input_sample_type == "right":
                sample_input = x + dx
            elif input_sample_type == "center":
                sample_input = x + 0.5 * dx
            else:
                raise Exception("Invalid input sample type")
            graph_point = self.input_to_graph_point(sample_input, graph)
            points = VGroup(*list(map(VectorizedPoint, [
                self.coords_to_point(x, 0),
                self.coords_to_point(x + width_scale_factor * dx, 0),
                graph_point
            ])))

            rect = Rectangle()
            rect.replace(points, stretch=True)
            if graph_point[1] < self.graph_origin[1] and show_signed_area:
                fill_color = invert_color(color)
            else:
                fill_color = color
            rect.set_fill(fill_color, opacity=fill_opacity)
            rect.set_stroke(stroke_color, width=stroke_width)
            rectangles.add(rect)
        return rectangles

    def get_riemann_rectangles_list(
        self,
        graph,
        n_iterations,
        max_dx=0.5,
        power_base=2,
        stroke_width=1,
        **kwargs
    ):
        """
        This method returns a list of multiple VGroups of Riemann
        Rectangles. The inital VGroups are relatively inaccurate,
        but the closer you get to the end the more accurate the Riemann
        rectangles become

        Parameters
        ----------
        graph (ParametricFunction)
            The graph whose area needs to be approximated
            by the Riemann Rectangles.
        
        n_iterations,
            The number of VGroups of successive accuracy that are needed.
        
        max_dx Union[int,float]
            The maximum change in x between two VGroups of Riemann Rectangles
        
        power_base Union[int,float=2]
        
        stroke_width : Union[int, float]
            The stroke_width of the border of the rectangles.
        
        **kwargs
            Any valid keyword arguments of get_riemann_rectangles.
        
        Returns
        -------
        list
            The list of Riemann Rectangles of increasing accuracy.
        """
        return [
            self.get_riemann_rectangles(
                graph=graph,
                dx=float(max_dx) / (power_base**n),
                stroke_width=float(stroke_width) / (power_base**n),
                **kwargs
            )
            for n in range(n_iterations)
        ]

    def get_area(self, graph, t_min, t_max):
        """
        Returns a VGroup of Riemann rectangles
        sufficiently small enough to visually
        approximate the area under the graph passed.
        
        Parameters
        ----------
        graph (ParametricFunction)
            The graph/curve for which the area needs to be gotten.
        
        t_min Union[int, float]
            The lower bound of x from which to approximate the area.
        
        t_max Union[int, float]
            The upper bound of x until which the area must be approximated.
        
        Returns
        -------
        VGroup
            The VGroup containing the Riemann Rectangles.
        """
        numerator = max(t_max - t_min, 0.0001)
        dx = float(numerator) / self.num_rects
        return self.get_riemann_rectangles(
            graph,
            x_min=t_min,
            x_max=t_max,
            dx=dx,
            stroke_width=0,
        ).set_fill(opacity=self.area_opacity)

    def transform_between_riemann_rects(self, curr_rects, new_rects, **kwargs):
        """
        This method is used to transform between two VGroups of Riemann Rectangles,
        if they were obtained by get_riemann_rectangles or get_riemann_rectangles_list.
        No animation is returned, and the animation is directly played.

        Parameters
        ----------
        curr_rects : VGroup
            The current Riemann Rectangles
        
        new_rects : VGroup
            The Riemann Rectangles to transform to.
        
        **kwargs
            added_anims
                Any other animations to play simultaneously.
        """
        transform_kwargs = {
            "run_time": 2,
            "lag_ratio": 0.5
        }
        added_anims = kwargs.get("added_anims", [])
        transform_kwargs.update(kwargs)
        curr_rects.align_submobjects(new_rects)
        x_coords = set()  # Keep track of new repetitions
        for rect in curr_rects:
            x = rect.get_center()[0]
            if x in x_coords:
                rect.set_fill(opacity=0)
            else:
                x_coords.add(x)
        self.play(
            Transform(curr_rects, new_rects, **transform_kwargs),
            *added_anims
        )

    def get_vertical_line_to_graph(
        self,
        x, graph,
        line_class=Line,
        **line_kwargs
    ):
        """
        This method returns a Vertical line from the x-axis to 
        the corresponding point on the graph/curve.

        Parameters
        ----------
        x Union[int,float]
            The x-value at which the line should be placed/calculated.

        graph (ParametricFunction)
            The graph on which the line should extend to.
        
        line_class (Line and similar)
            The type of line that should be used.
            Defaults to Line
        
        **line_kwargs
            Any valid keyword arguments of the object passed in "line_class"
            If line_class is Line, any valid keyword arguments of Line are allowed.
        
        Return
        ------
        An object of type passed in "line_class"
            Defaults to Line
        """
        if "color" not in line_kwargs:
            line_kwargs["color"] = graph.get_color()
        return line_class(
            self.coords_to_point(x, 0),
            self.input_to_graph_point(x, graph),
            **line_kwargs
        )

    def get_vertical_lines_to_graph(
        self, graph,
        x_min=None,
        x_max=None,
        num_lines=20,
        **kwargs
    ):
        """
        Obtains multiple lines from the x axis to the Graph/curve.
        
        Parameters
        ----------
        graph (ParametricFunction)
            The graph on which the line should extend to.
        
        x_min (Union[int, float])
            The lower bound from which lines can appear.
        
        x_max (Union[int, float])
            The upper bound until which the lines can appear.
        
        num_lines (Union[int, float])
            The number of lines (evenly spaced)
            that are needed.
        
        Returns
        -------
        VGroup
            The VGroup of the evenly spaced lines.
        
        """
        x_min = x_min or self.x_min
        x_max = x_max or self.x_max
        return VGroup(*[
            self.get_vertical_line_to_graph(x, graph, **kwargs)
            for x in np.linspace(x_min, x_max, num_lines)
        ])

    def get_secant_slope_group(
        self,
        x, graph,
        dx=None,
        dx_line_color=None,
        df_line_color=None,
        dx_label=None,
        df_label=None,
        include_secant_line=True,
        secant_line_color=None,
        secant_line_length=10,
    ):
        """
        This method returns a VGroup of (two lines 
        representing dx and df, the labels for dx and 
        df, and the Secant to the Graph/curve at a 
        particular x value.

        Parameters
        ----------
        x (Union[float, int])
            The x value at which the secant enters, and intersects
            the graph for the first time.
        
        graph (ParametricFunction)
            The curve/graph for which the secant must
            be found.
        
        dx (Union[float, int])
            The change in x after which the secant exits.
        
        dx_line_color (str)
            The line color for the line that indicates the change in x.
        
        df_line_color (str)
            The line color for the line that indicates the change in y.
        
        dx_label (str)
            The label to be provided for the change in x.
        
        df_label (str)
            The label to be provided for the change in y.
        
        include_secant_line (bool=True)
            Whether or not to include the secant line in the graph,
            or just have the df and dx lines and labels.
        
        secant_line_color (str)
            The color of the secant line.
        
        secant_line_length (Union[float,int=10])
            How long the secant line should be.
        
        Returns:
        --------
        VGroup
            Resulting group is of the form VGroup(
                dx_line,
                df_line,
                dx_label, (if applicable)
                df_label, (if applicable)
                secant_line, (if applicable)
            )
            with attributes of those names.
        """
        kwargs = locals()
        kwargs.pop("self")
        group = VGroup()
        group.kwargs = kwargs

        dx = dx or float(self.x_max - self.x_min) / 10
        dx_line_color = dx_line_color or self.default_input_color
        df_line_color = df_line_color or graph.get_color()

        p1 = self.input_to_graph_point(x, graph)
        p2 = self.input_to_graph_point(x + dx, graph)
        interim_point = p2[0] * RIGHT + p1[1] * UP

        group.dx_line = Line(
            p1, interim_point,
            color=dx_line_color
        )
        group.df_line = Line(
            interim_point, p2,
            color=df_line_color
        )
        group.add(group.dx_line, group.df_line)

        labels = VGroup()
        if dx_label is not None:
            group.dx_label = TexMobject(dx_label)
            labels.add(group.dx_label)
            group.add(group.dx_label)
        if df_label is not None:
            group.df_label = TexMobject(df_label)
            labels.add(group.df_label)
            group.add(group.df_label)

        if len(labels) > 0:
            max_width = 0.8 * group.dx_line.get_width()
            max_height = 0.8 * group.df_line.get_height()
            if labels.get_width() > max_width:
                labels.set_width(max_width)
            if labels.get_height() > max_height:
                labels.set_height(max_height)

        if dx_label is not None:
            group.dx_label.next_to(
                group.dx_line,
                np.sign(dx) * DOWN,
                buff=group.dx_label.get_height() / 2
            )
            group.dx_label.set_color(group.dx_line.get_color())

        if df_label is not None:
            group.df_label.next_to(
                group.df_line,
                np.sign(dx) * RIGHT,
                buff=group.df_label.get_height() / 2
            )
            group.df_label.set_color(group.df_line.get_color())

        if include_secant_line:
            secant_line_color = secant_line_color or self.default_derivative_color
            group.secant_line = Line(p1, p2, color=secant_line_color)
            group.secant_line.scale_in_place(
                secant_line_length / group.secant_line.get_length()
            )
            group.add(group.secant_line)

        return group

    def add_T_label(self, x_val, side=RIGHT, label=None, color=WHITE, animated=False, **kwargs):
        """
        This method adds to the Scene:
            -- a Vertical line from the x-axis to the corresponding point on the graph/curve.
            -- a small vertical Triangle whose top point lies on the base of the vertical line
            -- a TexMobject to be a label for the Line and Triangle, at the bottom of the Triangle.
        The scene needs to have the graph have the identifier/variable name self.v_graph.

        Parameters
        ----------
        x_val (Union[float, int])
            The x value at which the secant enters, and intersects
            the graph for the first time.
        
        side (np.ndarray())
        
        label (str)
            The label to give the vertline and triangle
        
        color (str)
            The hex color of the label.
        
        animated (bool=False)
            Whether or not to animate the addition of the T_label
        
        **kwargs
            Any valid keyword argument of a self.play call.
        """
        triangle = RegularPolygon(n=3, start_angle=np.pi / 2)
        triangle.set_height(MED_SMALL_BUFF)
        triangle.move_to(self.coords_to_point(x_val, 0), UP)
        triangle.set_fill(color, 1)
        triangle.set_stroke(width=0)
        if label is None:
            T_label = TexMobject(self.variable_point_label, fill_color=color)
        else:
            T_label = TexMobject(label, fill_color=color)

        T_label.next_to(triangle, DOWN)
        v_line = self.get_vertical_line_to_graph(
            x_val, self.v_graph,
            color=YELLOW
        )

        if animated:
            self.play(
                DrawBorderThenFill(triangle),
                ShowCreation(v_line),
                Write(T_label, run_time=1),
                **kwargs
            )

        if np.all(side == LEFT):
            self.left_T_label_group = VGroup(T_label, triangle)
            self.left_v_line = v_line
            self.add(self.left_T_label_group, self.left_v_line)
        elif np.all(side == RIGHT):
            self.right_T_label_group = VGroup(T_label, triangle)
            self.right_v_line = v_line
            self.add(self.right_T_label_group, self.right_v_line)

    def get_animation_integral_bounds_change(
        self,
        graph,
        new_t_min,
        new_t_max,
        fade_close_to_origin=True,
        run_time=1.0
    ):
        """
        This method requires a lot of prerequisites:
        self.area must be defined from self.get_area()
        self.left_v_line and self.right_v_line must be defined from self.get_v_line
        self.left_T_label_group and self.right_T_label_group must be defined from self.add_T_label

        This method will returna VGroup of new mobjects for each of those, when provided the graph/curve,
        the new t_min and t_max, the run_time and a bool stating whether or not to fade when close to
        the origin.

        Parameters
        ----------
        graph (ParametricFunction)
            The graph for which this must be done.
        
        new_t_min (Union[int,float])
            The new lower bound.
        
        new_t_max (Union[int,float])
            The new upper bound.
        
        fade_close_to_origin (bool=True)
            Whether or not to fade when close to the origin.
        
        run_time (Union[int,float=1.0])
            The run_time of the animation of this change.
        """
        curr_t_min = self.x_axis.point_to_number(self.area.get_left())
        curr_t_max = self.x_axis.point_to_number(self.area.get_right())
        if new_t_min is None:
            new_t_min = curr_t_min
        if new_t_max is None:
            new_t_max = curr_t_max

        group = VGroup(self.area)
        group.add(self.left_v_line)
        group.add(self.left_T_label_group)
        group.add(self.right_v_line)
        group.add(self.right_T_label_group)

        def update_group(group, alpha):
            area, left_v_line, left_T_label, right_v_line, right_T_label = group
            t_min = interpolate(curr_t_min, new_t_min, alpha)
            t_max = interpolate(curr_t_max, new_t_max, alpha)
            new_area = self.get_area(graph, t_min, t_max)

            new_left_v_line = self.get_vertical_line_to_graph(
                t_min, graph
            )
            new_left_v_line.set_color(left_v_line.get_color())
            left_T_label.move_to(new_left_v_line.get_bottom(), UP)

            new_right_v_line = self.get_vertical_line_to_graph(
                t_max, graph
            )
            new_right_v_line.set_color(right_v_line.get_color())
            right_T_label.move_to(new_right_v_line.get_bottom(), UP)

            # Fade close to 0
            if fade_close_to_origin:
                if len(left_T_label) > 0:
                    left_T_label[0].set_fill(opacity=min(1, np.abs(t_min)))
                if len(right_T_label) > 0:
                    right_T_label[0].set_fill(opacity=min(1, np.abs(t_max)))

            Transform(area, new_area).update(1)
            Transform(left_v_line, new_left_v_line).update(1)
            Transform(right_v_line, new_right_v_line).update(1)
            return group

        return UpdateFromAlphaFunc(group, update_group, run_time=run_time)

    def animate_secant_slope_group_change(
        self, secant_slope_group,
        target_dx=None,
        target_x=None,
        run_time=3,
        added_anims=None,
        **anim_kwargs
    ):
        """
        This method animates the change of the secant slope group  from
        the old secant slope group, into a new secant slope group.

        Parameters
        ----------
        secant_slope_group (VGroup)
            The old secant_slope_group
        
        target_dx Union[int, float]
            The new dx value.
        
        target_x Union[int, float]
            The new x value at which the secant should be.
        
        run_time Union[int,float=3]
            The run time for this change when animated.
        
        added_anims
            Any exta animations that should be played alongside.
        
        **anim_kwargs
            Any valid kwargs of a self.play call.

        NOTE: At least one of target_dx and target_x should be not None.
        """
        if target_dx is None and target_x is None:
            raise Exception(
                "At least one of target_x and target_dx must not be None")
        if added_anims is None:
            added_anims = []

        start_dx = secant_slope_group.kwargs["dx"]
        start_x = secant_slope_group.kwargs["x"]
        if target_dx is None:
            target_dx = start_dx
        if target_x is None:
            target_x = start_x

        def update_func(group, alpha):
            dx = interpolate(start_dx, target_dx, alpha)
            x = interpolate(start_x, target_x, alpha)
            kwargs = dict(secant_slope_group.kwargs)
            kwargs["dx"] = dx
            kwargs["x"] = x
            new_group = self.get_secant_slope_group(**kwargs)
            group.become(new_group)
            return group

        self.play(
            UpdateFromAlphaFunc(
                secant_slope_group, update_func,
                run_time=run_time,
                **anim_kwargs
            ),
            *added_anims
        )
        secant_slope_group.kwargs["x"] = target_x
        secant_slope_group.kwargs["dx"] = target_dx