matplotlib-devel Mailing List for matplotlib

Hi there,

I hit a strange but in the code for logarithmic plotting. Executing the 
following code:

----------------------------------
from matplotlib.matlab import *
plot([1.,2.],[0.01,0.2])
gca().set_yscale('log')
show()
----------------------------------

gives the following traceback:

------------------------------------
Traceback (most recent call last):
  File "./matplotlib-bug.py", line 4, in ?
    show()
  File 
"/home/nobbi/NNlab/install/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", 
line 68, in show
    manager.show()
  File 
"/home/nobbi/NNlab/install/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", 
line 284, in show
    self.canvas.draw()
  File 
"/home/nobbi/NNlab/install/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", 
line 135, in draw
    FigureCanvasAgg.draw(self)
  File 
"/home/nobbi/NNlab/install/lib/python2.3/site-packages/matplotlib/backends/backend_agg.py", 
line 310, in draw
    self.figure.draw(self.renderer)
  File 
"/home/nobbi/NNlab/install/lib/python2.3/site-packages/matplotlib/figure.py", 
line 254, in draw
    for a in self.axes: a.draw(renderer)
  File 
"/home/nobbi/NNlab/install/lib/python2.3/site-packages/matplotlib/axes.py", 
line 935, in draw
    self.transData.freeze()  # eval the lazy objects
ValueError: Cannot take log of nonpositive value
-------------------------------------

The appearance of this bug actually depends opn the ratio between the y-values 
given: if the factor exceeds 10, the code breaks:

[0.1,0.2] works
[0.01,0.02] works
[0.1,1.0] works
[0.1,2.0] breaks
[1.0,11.0] breaks

Also: the problem does not appear when using semilogy

I'm using cvs versions of matplotlib and Numeric on python 2.3.4

Greetings,
Norbert

-- 
_________________________________________Norbert Nemec
         Bernhardstr. 2 ... D-93053 Regensburg
     Tel: 0941 - 2009638 ... Mobil: 0179 - 7475199
           eMail: <No...@Ne...>

On Tue, 2004-11-09 at 12:24, Fernando Perez wrote:
> Just curious: can you comment on what's similar/different between 
> cairo and agg?  Is there significant duplication or do they target
> different problems? Would it make sense for these two projects to
> share code?  I worry a bit about the explosion of backends, esp.
> because of the maintainability burden it tends to cause in the long
> term.
Agg is written in C++, has been around for a while and is quite
mature/stable. Cairo is younger and has not yet made an "official"
release. It is written in C with language bindings available for Python,
Java, Perl and others. Agg and Cairo both aim to be platform
independent, and they overlap on many of their features. Apparently
OpenOffice, Mozilla and GTK+ are considering using Cairo in their
software, so it could become very popular.

Steve