Re: [Matplotlib-users] scipy.xplt to matplotlib

[John H. <jdh...@ac...>]

>>>>> "Fernando" == Fernando Perez <Fer...@co...> writes:

    Fernando> One word of caution: you'll notice that in the above,
    Fernando> the xplt script runs very fast, while the mpl one is
    Fernando> unacceptably slow (and it consumes a TON of cpu).  There
    Fernando> may be a trick to provide acceptable update speeds for
    Fernando> dynamically resized plots, but unfortunately I don't use
    Fernando> that kind of plotting much, so I can't really offer much
    Fernando> help there.

Yes, this will run extremely slow, because each plot command creates a
new matplotlib.lines.Line2D object, which at draw time means a new
transformation, a new graphics context, etc.  By the time you reach
the end of the loop, you'll have a ton of extra overhead in object
creation and function calls.

If possible, I suggest creating just two line objects and manipulating
their data directly, as in

from math import sin, cos
import matplotlib.numerix as nx
import pylab
pylab.ion()  # interactive on, so each plot updates the window

pylab.hold('on')
allt = [0]          # grow these lists and set the line data with them
allsin = [sin(0)]
allcos = [cos(0)]
lsin, = pylab.plot(allt, allsin, 'g+') # lsin is a Line2D instance
lcos, = pylab.plot(allt, allcos, 'ro') # lcos is a Line2D instance
pylab.xlabel('Time t[s]')
pylab.ylabel('Response')
pylab.axis([0,10,-1,1])
for t in nx.arange(0.1,10,0.1):
    allt.append(t)
    allsin.append(sin(t))
    allcos.append(cos(t))
    lsin.set_data(allt, allsin)
    lcos.set_data(allt, allcos)
    pylab.draw()

# to prevent the window from closing
raw_input()

    Fernando> I get the feeling that there's an O(N^2) problem
    Fernando> somewhere in there, because it seems to me that the plot
    Fernando> update slows down worse than linearly as more points are
    Fernando> added.  But I didn't really measure it, it's just a gut
    Fernando> feeling.

This will still be slower than xplt, but shouldn't be mind-numbingly
slow.  I have some concrete ideas on how to make animation faster, and
have started working on them, but don't have anything ready yet.

JDH