运行时错误:init_func 必须返回一系列 Artist 对象 [英] RuntimeError: The init_func must return a sequence of Artist objects

问题描述

我正在尝试在jupyter笔记本上测试Matplotlib动画示例，其示例如下:

I am trying to test a Matplotlib animation example on my jupyter notebook which is listed as following:

from matplotlib import animation
# solve the ode problem of the double compound pendulum again

from scipy.integrate import odeint
from numpy import cos, sin

g = 9.82; L = 0.5; m = 0.1

def dx(x, t):
    x1, x2, x3, x4 = x[0], x[1], x[2], x[3]

    dx1 = 6.0/(m*L**2) * (2 * x3 - 3 * cos(x1-x2) * x4)/(16 - 9 * cos(x1-x2)**2)
    dx2 = 6.0/(m*L**2) * (8 * x4 - 3 * cos(x1-x2) * x3)/(16 - 9 * cos(x1-x2)**2)
    dx3 = -0.5 * m * L**2 * ( dx1 * dx2 * sin(x1-x2) + 3 * (g/L) * sin(x1))
    dx4 = -0.5 * m * L**2 * (-dx1 * dx2 * sin(x1-x2) + (g/L) * sin(x2))
    return [dx1, dx2, dx3, dx4]

x0 = [np.pi/2, np.pi/2, 0, 0]  # initial state
t = np.linspace(0, 10, 250) # time coordinates
x = odeint(dx, x0, t)    # solve the ODE problem

fig, ax = plt.subplots(figsize=(5,5))

ax.set_ylim([-1.5, 0.5])
ax.set_xlim([1, -1])

pendulum1, = ax.plot([], [], color="red", lw=2)
pendulum2, = ax.plot([], [], color="blue", lw=2)

def init():
    pendulum1.set_data([], [])
    pendulum2.set_data([], [])

def update(n): 
    # n = frame counter
    # calculate the positions of the pendulums
    x1 = + L * sin(x[n, 0])
    y1 = - L * cos(x[n, 0])
    x2 = x1 + L * sin(x[n, 1])
    y2 = y1 - L * cos(x[n, 1])

    # update the line data
    pendulum1.set_data([0 ,x1], [0 ,y1])
    pendulum2.set_data([x1,x2], [y1,y2])

anim = animation.FuncAnimation(fig, update, init_func=init, frames=len(t), blit=True)

# anim.save can be called in a few different ways, some which might or might not work
# on different platforms and with different versions of matplotlib and video encoders
#anim.save('animation.mp4', fps=20, extra_args=['-vcodec', 'libx264'], writer=animation.FFMpegWriter())
#anim.save('animation.mp4', fps=20, extra_args=['-vcodec', 'libx264'])
#anim.save('animation.mp4', fps=20, writer="ffmpeg", codec="libx264")
anim.save('animation.mp4', fps=20, writer="avconv", codec="libx264")

plt.close(fig)

但是，当我在笔记本中运行单元格时，它给了我这个错误:

However, when I run the cell in notebook it gives me this error:

RuntimeError: The init_func must return a sequence of Artist objects.

我不太确定发生了什么..init函数没有发现任何错误.

I am not quite sure what is going on.. I don't see anything wrong in the init function.

此示例的链接:https://github.com/jrjohansson/scientific-python-lectures/blob/master/Lecture-4-Matplotlib.ipynb它位于本笔记本的最底部.

The link to this example: https://github.com/jrjohansson/scientific-python-lectures/blob/master/Lecture-4-Matplotlib.ipynb It is at the very bottom of this notebook.

推荐答案

如错误所示，例如在 simple_animation 示例 中，但也来自

As the error suggests, and as can be seen e.g. in the simple_animation example, but also from the FuncAnimation documentation, the init_func as well as the updating func are supposed to return an iterable of artists to animate.

文档并没有说这实际上仅在使用 blit=True 时才需要，但是由于您在这里使用了 blitting，因此绝对需要.

The documentation does not say that this is actually only needed when using blit=True, but since you are using blitting here, it is definitely needed.

因此，您需要做的是让 init 函数以及 update 函数返回要动画的两行

What you would therefore need to do is to let the init function as well as the update function return the two lines which get animated

def init():
    pendulum1.set_data([], [])
    pendulum2.set_data([], [])
    return pendulum1, pendulum2, 

def update(n): 
    # n = frame counter
    # calculate the positions of the pendulums
    x1 = + L * sin(x[n, 0])
    y1 = - L * cos(x[n, 0])
    x2 = x1 + L * sin(x[n, 1])
    y2 = y1 - L * cos(x[n, 1])

    # update the line data
    pendulum1.set_data([0 ,x1], [0 ,y1])
    pendulum2.set_data([x1,x2], [y1,y2])

    return pendulum1, pendulum2, 

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