Animating a function where function parameters change with time using FuncAnimation

Question

I am trying to animate a one-dimensional function where the function inputs are same but function parameters are changing with time. The function I am trying to animate is

f(x)=sin(a* pi * x)/(b*x)+ (x-1)^4

Here the data to be plotted is same, but a, b are changing with every update.I am using python and matplotlib library. My initial attempt is as follows:

fig,ax = plt.subplots()
line, = ax.plot([],[])

def animate(i,func_params):
    x = np.linspace(-0.5,2.5,num = 200)
    a=func_params[i][0]
    b=func_params[i][1]
    y=np.sin(a*math.pi*x)/b*x + (x-1)**4
    line.set_xdata(x)
    line.set_ydata(y)
    return line,

ani = animation.FuncAnimation(fig,animate,frames=len(visualize_pop),fargs=(visualize_func,),interval = 100,blit=True)
plt.show()

The above code is not plotting anything.

EDIT: Updated code based on comment.

The error tells you that the `Line2D` is not iterable. So you can deduce that you need to return something iterable. Hence, `return line,` (note the comma). — ImportanceOfBeingErnest, Nov 30 '18 at 00:49
That may have a different reason. But it'll get rid of the error you inquire about. Since your code isn't runnable, that is all one can say at this stage. — ImportanceOfBeingErnest, Nov 30 '18 at 00:51
What exactly does "not plotting anything" mean? Do you not get any figure window? In that case you need to call `plt.show()` at the end. — ImportanceOfBeingErnest, Nov 30 '18 at 00:53
You add a plot via `fig.add_subplot(111)`. So independent of the incomplete code you have, there must be an axes. — ImportanceOfBeingErnest, Nov 30 '18 at 01:04
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/184502/discussion-between-loukit-khemka-and-importanceofbeingernest). — , Nov 30 '18 at 01:08

score -1 · Accepted Answer · answered Nov 30 '18 at 11:17

Your problem is that with plot([],[]) you give matplotlib no data and therefore no way do determine the limits of the axes. Therefore it uses some default values which are way out of the range of the data you actually want to plot. Therefore you have two choices:

1) Set the limits to some values that will contain all your plotted data for all cases, e.g.

ax.set_xlim([-0.5,2.5])
ax.set_ylim([-2,6])

2) Let ax compute the limits automatically each frame and re-scale the plot see here using these two commands within your animate function (note that this option only works correctly if you turn blitting off):

ax.relim()
ax.autoscale_view()

Here still a completely working version of your code (the commands for solution (1) are commented out and I changed some of the notations):

from matplotlib import pyplot as plt
from matplotlib.animation import FuncAnimation
import numpy as np

fig,ax = plt.subplots()
x = np.linspace(-0.5,2.5,num = 200)
line, = ax.plot([],[])

#ax.set_xlim([-0.5,2.5])
#ax.set_ylim([-2,6])

##assuming some parameters, because none were given by the OP:
N = 20
func_args = np.array([np.linspace(1,2,N), np.linspace(2,1,N)])

def animate(i,func_params):
    a=func_params[0,i]
    b=func_params[1,i]
    y=np.sin(a*np.pi*x)/b*x + (x-1)**4
    line.set_xdata(x)
    line.set_ydata(y)
    ax.relim()
    ax.autoscale_view()
    return line, ax

##blit=True will not update the axes labels correctly
ani = FuncAnimation(
    fig,animate,frames=N, fargs=(func_args,),interval = 100 #, blit=True
)
plt.show()

Animating a function where function parameters change with time using FuncAnimation

1 Answers1