Re: [Matplotlib-users] tick-marks feature request

[John H. <jdh...@ac...>]

>>>>> "Darren" == Darren Dale <dd...@co...> writes:

    Darren> Hi All, My research group submitted a paper for
    Darren> publication in a journal, and one of the requested changes
    Darren> was having the tick-marks formatted like $1x10^{-4}$ (for
    Darren> the latex-ers out there) rather than 1e-4, which was
    Darren> considered an unnecessary use of mathematical jargon. I
    Darren> wasn't the lead author on this particular paper, and
    Darren> therefore the plots were not created using Python and
    Darren> MPL. But I think this is a pretty standard formatting
    Darren> requirement in the scientific community. Would the
    Darren> creators of Matplotlib consider an option to format the
    Darren> ticks like this (does this capability exist and I havent
    Darren> found it yet)?

Yes, this would be nice.  Of course, you can manually format the ticks
using mathtext, eg, 

    from matplotlib.matlab import *

    rc('tick', labelsize=15)

    a=[8E8,10E8, 15E8]
    plot(a,a)

    ticks = arange(8,16)
    labels = ['$%d^{8}$'%val for val in ticks]
    set(gca(), xticks=ticks*1e8, yticks=ticks*1e8,
               xticklabels=labels, yticklabels=labels)

    show()

but it would be nice to provide some automatic facilities for this.

    Darren> In Matlab, when the tick labels require scientific
    Darren> notation, only the decimal component is listed in each
    Darren> tick label, and the exponential part is printed at the end
    Darren> of the axis. In Igor, the exponential part can be included
    Darren> in the y-axis label. Finally, one problem with formatting
    Darren> tick labels is how to deal with data spanning small
    Darren> ranges, but with large offsets, like
    Darren> array(range(10))+1e10. Maybe there is an interest in
    Darren> removing the offset from each tick label, and including it
    Darren> elsewhere in the figure? Then again, maybe that's getting
    Darren> too complicated.

This would definitely be a nice feature.  It would require a little
architectural change in the formatter.  Basically the formatter would
need to provide an additional method, eg get_offset, which would
return None (the current default) or a string like '$10^{-23}$.  The
axis, which calls the formatter, could check this value, and if not
None, render it to the proper place (eg left of x axis).  I could help
you with this part.  Below I'll include a script example showing how
to plot a tick offset which you can currently use for figures.
Basically, we'd just want to automate something along these lines.

    Darren> Is this attractive to the Matplotlib Gurus and Users? If
    Darren> so, is it something I could work on, or would it be best
    Darren> left to the masters?

There's only one path to becoming a master, of course, which is to
dive in.  It would be great if you work on this.  Getting ticking
right is pretty hard since there are so many pathological cases out
there.  But it looks like you work with that kind of data so you'll be
in a good position to find and fix the problem spots.  I think you
should take two approaches: 1) clean up the existing Locators and
Formatters when you find bugs and 2) define some new ones.  It
shouldn't be too hard to define a new formatter that does the mathtext
formatting for exponential ticking you've alluded to above.

The only (minor) downside to doing mathtext formatting is that the
font is likely different than non-mathtext on your figure.  There are
two ways to solve this: use the cmr font as the default for the entire
figure or better, support mathtext layout (super/subscripting) for any
font.  Right now we use the computer modern fonts for mathtext because
they have all the symbols, but there is no reason (other than time)
that we can't use the mathtext layout algorithms for
super/subscripting of non symbol fonts.  


Let me know how I can help...

JDH

# use an exponential tick offset
from matplotlib.matlab import *

rc('tick', labelsize=12)

a=[8E8,10E8, 15E8]
plot(a,a)

ticks = arange(8,16)
labels = ['%d'%val for val in ticks]

# place the offset in axes coords
t = text(-.075, -.075, r'$10^{8}\times$',
         transform=gca().transAxes,
         fontsize=14)
t.set_clip_on(False)

set(gca(), xticks=ticks*1e8, yticks=ticks*1e8,
    xticklabels=labels, yticklabels=labels)


show()