Dynamic plot in python

Question

I'm trying to create a plot in Python where the data that is being plotted gets updated as my simulation progresses. In MATLAB, I could do this with the following code:

t = linspace(0, 1, 100);
figure
for i = 1:100
x = cos(2*pi*i*t);
plot(x)
drawnow
end

I'm trying to use matplotlib's FuncAnimation function in the animation module to do this inside a class. It calls a function plot_voltage which recalculates voltage after each timestep in my simulation. I have it set up as follows:

import matplotlib.pyplot as plt
import matplotlib.animation as animation

def __init__(self):
    ani = animation.FuncAnimation(plt.figure(2), self.plot_voltage)
    plt.draw()

def plot_voltage(self, *args):
    voltages = np.zeros(100)
    voltages[:] = np.nan

    # some code to calculate voltage

    ax1 = plt.figure(2).gca()
    ax1.clear()
    ax1.plot(np.arange(0, len(voltages), 1), voltages, 'ko-')`

When my simulation runs, the figures show up but just freeze. The code runs without error, however. Could someone please let me know what I am missing?

Thanks, @cphlewis. The problem with that solution is that if I have another function, say count() which simply counts up the positive integers, and I run this after plt.show(), count() won't run until I close the plot. Replacing plt.show() with plt.draw() causes the plot not to show up at all, but then count() runs. How can I have the plot update while the program continues and count() runs? My backend is Qt5Agg with interactive mode on. — Vivek Subramanian
– Vivek Subramanian, Commented Mar 3, 2017 at 1:54
In the third solution, update() would call both your count(), so the plotting continues. — cphlewis
– cphlewis, Commented Mar 3, 2017 at 1:56
Thanks, @cphlewis. When I include the count() function in update(), the code runs and the plot shows up, but the window just freezes and nothing is displayed. My code is here. — Vivek Subramanian
– Vivek Subramanian, Commented Mar 3, 2017 at 2:06
Don't ever use while True in a program that requires user interaction. — ImportanceOfBeingErnest
– ImportanceOfBeingErnest, Commented Mar 3, 2017 at 11:22

ImportanceOfBeingErnest · Accepted Answer · 2017-03-07 07:47:55Z

3

Here is a translation of the matlab code into matplotlib using FuncAnimation:

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

t = np.linspace(0, 1, 100)
fig = plt.figure()
line, = plt.plot([],[])

def update(i):
    x = np.cos(2*np.pi*i*t)
    line.set_data(t,x)

ani = animation.FuncAnimation(fig, update, 
                frames=np.linspace(1,100,100), interval=100)
plt.xlim(0,1)
plt.ylim(-1,1)
plt.show()

answered Mar 7, 2017 at 7:47

ImportanceOfBeingErnest

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2 Comments

Vivek Subramanian Over a year ago

Thanks, but your comment above is right - I should have been clearer. I have a simulation in which parameters of an object are being updated. Every time an update is performed, I want to plot their values. Here is a minimal example. I don't necessarily need to use the animation package. It's just something I was trying. When I run this example, the figures do not render, and the window doesn't respond. When I ctrl+c the Terminal, the figures plot but the program stops. Any thoughts on the best way to do this?

ImportanceOfBeingErnest Over a year ago

I commented below the code at GiHubGist.

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