I am aware of these questions: (A), (B) and (C) - all of which address parts of my problem.

I have also read the Animations Cookbook

My questions, however, seem not to be addressed in any of the above.

I wish to plot objective functions returned by an optimizer while the optimizer is running. I do not know in advance how many iterations the optimizer will run. Independent of how I get the array containing the objective functions, the problem can be isolated in this minimal example:

```
import numpy as np
import matplotlib.pyplot as plt
SIZE = 50
R1 = 0.5
R2 = 0.75
plt.ion()
fig = plt.figure()
ax = fig.add_subplot(111)
fig.canvas.set_window_title('broken spiral')
for i in range(0, SIZE):
A.append(R1 * i * np.sin(i))
B.append(R2 * i * np.cos(i))
line1, = ax.plot(A,'-k',label='black')
line2, = ax.plot(B,'-r',label='red')
legend = ax.legend(loc=0)
plt.draw()
plt.savefig('test_broken_spiral.png')
```

Here the plot is only 'pseudo'-updated. What really happens is that for each iteration a new line for `A`

and `B`

is generated, overlying with the original one, but also generating a new legend entry. After 50 iterations, I have 100 lines and 100 legend entries.

I tried this next:

```
for i in range(0, SIZE):
A.append(R1 * i * np.sin(i))
B.append(R2 * i * np.cos(i))
if i == 0:
line1, = ax.plot(A,'-k',label='black')
line2, = ax.plot(B,'-r',label='red')
legend = ax.legend(loc=0)
plt.draw()
else:
line1.set_ydata(A)
line2.set_ydata(B)
plt.draw()
plt.savefig('test_broken_spiral.png')
```

Unfortunately, this plot has completely messed up axis.

I put the `if i == 0`

statement in, because I do not know the number of iterations in advance (yes, I do in this case, but not in the application this is targeted at) and somehow have to 'initialize' the plot and legend.

My questions can be summarized as follows:

1.) How do I update my plot? If I run the optimizer for 10,000 iterations, I don't want 10,000 overlying lines in my plot (filesize).

2.) Where do I place the `legend`

command?

I'm running python 2.6.6 and matplotlib 0.99.1.1

Edit:

This seems to be a similar question, with the same unanswered issue.

Just make the line objects with empty data outside of your loop:

```
line1, = ax.plot([], [],'-k',label='black')
line2, = ax.plot([], [],'-r',label='red')
ax.legend()
for i in range(0, SIZE):
A.append(R1 * i * np.sin(i))
B.append(R2 * i * np.cos(i))
line1.set_ydata(A)
line1.set_xdata(range(len(A)))
line2.set_ydata(B)
line2.set_xdata(range(len(B)))
ax.relim()
ax.autoscale_view()
plt.draw()
```

You can probably be a bit more clever about updating your `xdata`

.

For a more complete example see here and the full gallery of animation examples.

Licensed under: CC-BY-SA with attribution

Not affiliated with: Stack Overflow