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The following test program dies with an error when used with the
arguments shown -- but cutting back the argument lists by even one
element allows it to work OK.  So does taking out the hold(False).
This is with Mac OS X, Apple Python 2.3,  Matplotlib version 0.71,
  __revision__ '$Revision: 1.30 $'

--Eliot Smith, Indiana University

#------begin test program--------
from pylab import *

a =[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 
21, 22]
at=[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 
21]

b =[0.04, 0.06, 0.05, 0.07, 0.03, 0.07, 0.08, 0.05, 0.02, 0.07, 0.07, 
0.04, 0.06, 0.03, 0.01, 0.03, 0.01, 0.04, 0.03, 0.04, 0.04]
bt=[0.04, 0.06, 0.05, 0.07, 0.03, 0.07, 0.08, 0.05, 0.02, 0.07, 0.07, 
0.04, 0.06, 0.03, 0.01, 0.03, 0.01, 0.04, 0.03, 0.04]

print len(a), len(b)

hold(False)
figure(1)
loglog(a, b, 'bo')
show()

# this fails with
#File "/platlib/matplotlib/axes.py", line 1169, in draw
#ValueError: Cannot take log of nonpositive value

#replacing a, b in the loglog call with at, bt (lists just one
#item shorter) it no longer fails


# Mac OS X, Apple Python 2.3
# Matplotlib version 0.71
# __revision__ '$Revision: 1.30 $'

#----------end test program--------------------

I am unable to get matplotlib animations to work properly. Some of the data from
the previous frame is getting included.

I have included some example code that shows this. When draw() is called in the
loop, it draws the data from the previous frame for y<0.15 (ca), and from the
current frame for larger y. The final show() does *not* lag even if set_ydata
has not been called since the last draw().

This is with version 0.72. Any ideas about what is happening?

-- code follows

# animate increasing terms in fourier expansion of y=x
from pylab import *
from time import sleep

samples = 1000
max_k   = 3

x = arange(0.0, 1.0, 1.0/samples)

s = zeros((max_k,samples), Float)

for k in range(1,max_k):
    s[k] = s[k-1]+(-1)**(k+1)*sin(pi*x*k)/k

ion() # to force window creation
line, = plot(x, x*1.3, linewidth=1.0)
grid(True)
ioff()

for k in range(1,max_k):
    line.set_ydata(2/pi*s[k])
    title('k = '+str(k))
    draw()
    sleep(1)

show()

-- 
j