On Wednesday 15 August 2007 03:18:25 pm you wrote:
> On Wed, Aug 15, 2007 at 09:57:21AM -0400, Darren Dale wrote:
> > On Tuesday 14 August 2007 07:35:43 pm Darren Dale wrote:
> > > I'm developing an application for work and need to plot some spectra on
> > > a logscale. I can recreate my problem with embedding_in_qt4, by
> > > replacing MyDynamicMplCanvas.compute_initial_figure with this:
> > >
> > > def compute_initial_figure(self):
> > > self.axes.plot([0, 1, 2, 3], [1, 2, 0, 4], 'r')
> > > self.axes.set_yscale('log')
> > >
> > > [...]
> > > File
> > > "/usr/lib64/python2.5/site-packages/matplotlib-0.90.1_r3709-py2.5-linux
> > >-x86 _64.egg/matplotlib/axes.py", line 1664, in set_ylim
> > > raise ValueError('Cannot set nonpositive limits with log
> > > transform') ValueError: Cannot set nonpositive limits with log
> > > transform
> > >
> > > I get that error even if I modify the update figure function so there
> > > is no possibility of zeros occuring in the data
> >
> > I have tracked this back through axes.cla(), which is called when
> > axes._hold is False, to axis.cla(). axis.cla() resets the locators, but
> > the transforms are still set to mtrans.LOG10. Since plot is called by
> > loglog, and semilog*, it shouldn't be using any methods that modify
> > locators. If cla() resets the transforms, then the behavior of plot will
> > be different, preserving log transforms when hold is True, but changing
> > to linear transforms when hold is False.
> >
> > I wonder if cla() is trying to do too much. Maybe the initial setting of
> > locators should be moved out of cla(), which is called by Axes.__init__,
> > and into Axis.__init__. Then calls to cla() will preserve the scaling,
> > and the behavior of plot() will be consistent, regardless of the whether
> > hold is enabled or not.
>
> The other option is to do something sensible when axes limits are
> negative on the log scale.
Thats a seperate, but important issue. In the case I described, the state of
the plot becomes a mash of log transforms and linear locators.
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