[matplotlib-devel] axis / loglog / semilog issues

[Todd M. <jm...@st...>]

Hi,

JC Hsu reported that loglog() was broken with numarray and was raising
an exception due to an "illegal" call to __nonzero__().  

>>> from matplotlib.matlab import *
>>> loglog(arange(2,800))
[<matplotlib.lines.Line2D instance at 0x41e0ae8c>]
>>> show()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", line 57, in show
    manager.show()
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", line 163, in show
    self.canvas.show()
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", line 115, in show
    FigureCanvasAgg.draw(self)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_agg.py", line 353, in draw
    self.figure.draw(self.renderer)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/artist.py",
line 88, in draw
    self._draw(renderer, *args, **kwargs)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/figure.py",
line 89, in _draw
    for a in self.axes: a.draw(renderer)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/artist.py",
line 88, in draw
    self._draw(renderer, *args, **kwargs)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/axes.py",
line 531, in _draw
    self.xaxis.draw(renderer)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/artist.py",
line 88, in draw
    self._draw(renderer, *args, **kwargs)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/axis.py",
line 378, in _draw
    locs = self.get_ticklocs()
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/axis.py",
line 596, in get_ticklocs
    ind = nonzero(ticklocs>=10.0**vmin * ticklocs<=10.0**vmax)
  File
"/home/jmiller/work/lib/python2.3/site-packages/numarray/generic.py",
line 474, in __nonzero__
    raise RuntimeError("An array doesn't make sense as a truth value. 
Use sometrue(a) or alltrue(a).")
RuntimeError: An array doesn't make sense as a truth value.  Use
sometrue(a) or alltrue(a).

Confusingly, the explicit call to nonzero() is not what is causing the
numarray problem.  The problem is an implicit call to
NumArray.__nonzero__() resulting from the range expression.  I found I
could "fix" the numarray exception by adding parens to the range
expression:

nonzero((ticklocs >= 10.0**ymin) * (ticklocs <= 10.0**ymax))

Evaluating using the attached script,  I got the impression that while
numarray was raising an exception,  Numeric was giving an unintended /
wrong answer.    Anyway,  I wanted to get a second opinion before
committing anything since it smacks of hacking matplotlib to work around
numarray limitations.

Lastly,  assuming the parens are correct,  there is still a problem with
the log functions which I haven't looked at yet:

>>> loglog(arange(2,800))
[<matplotlib.lines.Line2D instance at 0x41e0ae8c>]
>>> show()
opened /home/jmiller/work/share/matplotlib/Vera.ttf
log iterable warning, non-positive data ignored
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", line 57, in show
    manager.show()
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", line 163, in show
    self.canvas.show()
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_tkagg.py", line 115, in show
    FigureCanvasAgg.draw(self)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/backends/backend_agg.py", line 353, in draw
    self.figure.draw(self.renderer)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/artist.py",
line 88, in draw
    self._draw(renderer, *args, **kwargs)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/figure.py",
line 89, in _draw
    for a in self.axes: a.draw(renderer)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/artist.py",
line 88, in draw
    self._draw(renderer, *args, **kwargs)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/axes.py",
line 541, in _draw
    line.draw(renderer)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/artist.py",
line 88, in draw
    self._draw(renderer, *args, **kwargs)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/lines.py",
line 184, in _draw
    self._lineFunc(renderer, gc, xt, yt)
  File
"/home/jmiller/work/lib/python2.3/site-packages/matplotlib/lines.py",
line 308, in _draw_solid
    renderer.draw_lines(gc, xt,yt)
ValueError: x and y must be equal length sequences



Regards,
Todd