[Matplotlib-users] Problem with linear plot after semilog plot

[Lorenzo I. <lor...@gm...>]

Dear All,
I am a bit puzzled at an unusual problem I am experiencing.
Fundamentally, I call a couple of functions and I plot some data.
First, I create a semilog plot using pylab.semilogx, then I make a
normal linear plot.
But, in the second case I get an error message:

Traceback (most recent call last):
  File "./air-mean-free-path.py", line 206, in ?
    pylab.plot((diam_seq*1e9),K_bis,linewidth=2.)
  File "/usr/lib/python2.4/site-packages/matplotlib/pylab.py", line
2027, in plot
    ret =  gca().plot(*args, **kwargs)
  File "/usr/lib/python2.4/site-packages/matplotlib/axes.py", line 2131, in plot
    self.autoscale_view(scalex=scalex, scaley=scaley)
  File "/usr/lib/python2.4/site-packages/matplotlib/axes.py", line
985, in autoscale_view
    self.set_xlim(XL)
  File "/usr/lib/python2.4/site-packages/matplotlib/axes.py", line
1220, in set_xlim
    raise ValueError('Cannot set nonpositive limits with log transform')
ValueError: Cannot set nonpositive limits with log transform


Which seems to be dealing with a semilog plot again, but that is no
longer the case.
What is going on? I am using the pylab.hold(False) command at the end
of each plot in order not to mess everything up.
Below there is the code producing the bug. If I go, after the 1st
semilog plot, for another semilog plot, everything is fine and no
error is generated.




K_thermo=K_talbot_test(T,knudsen,Ra)

pylab.semilogx(knudsen,K_thermo,linewidth=2.)
pylab.xlabel('knudsen number',fontsize=20.)
pylab.ylabel('K_th',fontsize=20.)
pylab.title('Thermophoretic coefficient',fontsize=20.)
pylab.grid(True)
pylab.savefig('thermophoretic_coefficient')

pylab.hold(False)



diam_seq=pylab.load("diameter_sequence")

diam_seq=diam_seq/1e9

print 'the shape of diam_seq is', shape(diam_seq)



K_bis=K_talbot(T)

print 'the shape of k_bis is', shape(K_bis)

#pylab.semilogx((diam_seq*1e9),K_bis,linewidth=2.)
pylab.plot((diam_seq*1e9),K_bis,linewidth=2.)
# with the plot command I run into trouble, with semilogx everything
is fine instead.

pylab.xlabel('diameter [nm]',fontsize=20.)
pylab.ylabel('K_th',fontsize=20.)
#pylab.legend(('prey population','predator population'))
pylab.title('Thermophoretic coefficient at T=350K',fontsize=20.)
pylab.grid(True)
pylab.savefig('thermophoretic_coefficient_vs_particle_diameter')

pylab.hold(False)

Does anybody have a clue at what is going on? I am sure it must be
something quick to fix.
Many thanks

Lorenzo