Re: [matplotlib-devel] auto log and key press

[Fernando P. <Fer...@co...>]

John Hunter wrote:

> If you have data points really close to 0, eg 
> 
>     1 >>> x = arange(-2.00, 10, 0.01)
> 
>     2 >>> amin(abs(x))
>     Out[2]: 4.163336342344337e-17
> 
> You may a heavy performance price because so many decades are plotted,
> each with minor ticks, and ticks are expensive in the current impl.

I had a look at gnuplot's strategy:

planck[~]> npy

In [1]: x = frange(1e-40, 10, npts=1003)

In [2]: gp('set logscale y')

In [3]: plot x,filename='logplotex.eps'


The result is here:

http://amath.colorado.edu/faculty/fperez/tmp/logplotex.eps

They seem to plot a maximum of 11 major ticks (that's what I'm guessing from a 
bunch of tests).  When it fits, each major tick is a decade, but at some point 
their algorithm switches over (like in my example) to every 3rd, 5th, 
whatever-th decade, and the minor ticks become decade ticks themselves.  When 
this happens, there are no logarithmically spaced ticks any more, obviously.

This is overall a nice approach, I think.  I have quite a few plots which 
cover 30 decades, and in matplotlib the result looks very crowded, while 
gnuplot's enforcement of a max of 11 (or whatever) major ticks gives a clean 
looking plot.

Gnuplot has many problems (hence my switch -finally- to mpl), but it has over 
a decade of fine-tuning of its behavior and interface, so it's not a bad 
source of inspiration.  It is mature and robust, and many of the things it 
does, it does really well.  I'll keep bringing up areas where I feel we can 
benefit from it (I know it reasonably well) as I move all my code over to mpl.

Cheers,

f