Re: [matplotlib-devel] plot() with a nearly-constant sequence doesn't always work

[Eric F. <ef...@ha...>]

On 05/25/2012 12:46 PM, Dan Drake wrote:
> Hello matplotlib developers,
>
> In Sage, we've run into a problem with plotting a sequence whose
> y-values change by very small amounts. Here's an example that doesn't
> use anything from Sage:
>
> import pylab
> pylab.plot([0, 1], [0, 1e-14])
> pylab.savefig("works.png")
> pylab.close()
> pylab.plot([0, 1], [1, 1+1e-14])
> pylab.savefig("fails.png")
> pylab.close()
>
> We're using matplotlib 1.1. Here's a trac ticket where we are working on
> this: http://trac.sagemath.org/sage_trac/ticket/11973. One of our
> developers suspects matplotlib.ticker.MaxNLocator.bin_boundaries but we
> don't really know.

Dan,

I think the behavior is coming from a threshold value of 1e-12 in 
ticker.scale_range.  This needs more thought than I can give it at the 
moment, but perhaps you could file a ticket on the github mpl site.

Note that even if this threshold behavior is removed, there is another 
one waiting in the wings behind it, with a default value of 1e-16, used 
to decide whether a range is singular; if it is, then it gets expanded.

Eric

>
> Thanks for any help or comments!
>
> Dan