matplotlib-devel Mailing List for matplotlib

On Mon, 2004年04月05日 at 18:32, John Hunter wrote:
> >>>>> "Todd" == Todd Miller <jm...@st...> writes:
> 
> Todd> Confusingly, the explicit call to nonzero() is not what is
> Todd> causing the numarray problem. The problem is an implicit
> Todd> call to NumArray.__nonzero__() resulting from the range
> Todd> expression. I found I could "fix" the numarray exception by
> Todd> adding parens to the range expression:
> 
> Todd> nonzero((ticklocs >= 10.0**ymin) * (ticklocs <= 10.0**ymax))
> 
> 
> I wasn't able to replicate your problem in ticklocs.py on my system
> (could be a version issue?).
Reproducing the exception requires using numarray-0.9. Also, 
ticklocs.py is coded to demonstrate the unexpected Numeric results
rather than the numarray exception to there is a try/except block which
passes the numarray exception on to parenthesized code.
> Ie, the following works fine for me; I
> assume it generated a RuntimeError for you based on your example code.
> 
> 
> ______________________________________________________________________
> In any case, in general I try to avoid using multiplication for
> logical arrays because it sometimes produces surprising results. I
> think here we want
> 
> ind = nonzero(logical_and(ticklocs>=10.0**vmin ,
> ticklocs<=10.0**vmax))
> 
This is clearer and unambiguous.
> 
> Todd> Lastly, assuming the parens are correct, there is still a
> Todd> problem with the log functions which I haven't looked at
> Todd> yet:
> 
> >>>> loglog(arange(2,800))
> 
> Here's what's going on under the hood
> 
> You are using the single arg form of plot with log scaling for both
> axes. The y values are arange(2,800) and the x values are implicit:
> arange(len(y)). Since this starts with 0, when take the log of zero
> in loglog, you are in a world of pain. The current version of
> matplotlib warns but then tries to go ahead, which generates the
> error. Specifically, it took the positive parts of x but left y
> alone, resulting in the unequal sized array problem.
> 
> I changed the code to raise rather than warn. You now get the more
> helpful error message
> 
> ValueError: Cannot take log of negative data
> 
Makes sense. Thanks for the explanation.
> Both changes in CVS.
> 
> JDH
Regards,
Todd
-- 
Todd Miller <jm...@st...>