#4529: Implement plots with logarithmic scale
----------------------------------+-----------------------------------------
Reporter: ronanpaixao | Owner: ronanpaixao
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.1
Component: graphics | Resolution:
Keywords: plot log scale | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: 12974 | Stopgaps:
----------------------------------+-----------------------------------------
Changes (by ppurka):
* dependencies: => 12974
Old description:
> Currently plot() has no option to use logarithmic scales.
>
> One workaround is to use matplotlib directly, with its semilogy(),
> semilogx() and loglog() functions, but that wouldn't produce plots with
> the customisations implemented in sage.
> Another workaround is messing with the plot figure like:
>
> {{{
> #!python
> import pylab
> p=plot(x,marker='.')
> f=pylab.figure()
> f.gca().set_xscale('log')
> p.save(figure=f)
> }}}
>
> But that creates two problems:
>
> * The first problem is that the adaptive choosing of points just
> considers linear scale, so the points get too much spaced apart in the
> beginning of the plot and too close in the end.
> * The second problem relates to the axis, which, for the same reason,
> isn't located right.
>
> Also, this requires the user to know how to deal with figures, which is
> not directly exposed by sage.
>
> There are some possibilities to fix that:
> 1. Make plot() detect if the figure changes the scales and modify the
> adaptive algorithm and the axis codes accordingly
> 2. Create a kwarg to tell plot() to implement the scale-change
> internally
> 3. Create other functions to use loglog(), semilogx() and semilogy()
> 4. Many (or all) of the above together, since they aren't mutually
> exclusive
>
> From what I noticed, Mathematica implements the separate functions way,
> but it may be better to fix the issue in plot() itself and if the other
> functions are wanted, just make it so that they call plot() with the
> correct arguments
New description:
Attached is a patch which introduces log scale to `Graphics()` class.
Apply the following patches in the specified order. `SAGE_ROOT` is the
directory where the sage installation is present.
{{{
cd SAGE_ROOT/devel/sage
../../sage -hg qimport -P http://trac.sagemath.org/sage_trac/raw-
attachment/ticket/12974/trac_12974-fix_graphics_attributes_and_reorder_args.patch
../../sage -hg qimport -P http://trac.sagemath.org/sage_trac/raw-
attachment/ticket/12974/trac_12974-refactor_and_whitespace_cleanups.patch
../../sage -hg qimport -P http://trac.sagemath.org/sage_trac/raw-
attachment/ticket/4529/trac_4529-add_logscale_to_Graphics.patch
../../sage -b
}}}
----
'''OLD DISCUSSION BELOW :)'''
Currently plot() has no option to use logarithmic scales.
One workaround is to use matplotlib directly, with its semilogy(),
semilogx() and loglog() functions, but that wouldn't produce plots with
the customisations implemented in sage.
Another workaround is messing with the plot figure like:
{{{
#!python
import pylab
p=plot(x,marker='.')
f=pylab.figure()
f.gca().set_xscale('log')
p.save(figure=f)
}}}
But that creates two problems:
* The first problem is that the adaptive choosing of points just
considers linear scale, so the points get too much spaced apart in the
beginning of the plot and too close in the end.
* The second problem relates to the axis, which, for the same reason,
isn't located right.
Also, this requires the user to know how to deal with figures, which is
not directly exposed by sage.
There are some possibilities to fix that:
1. Make plot() detect if the figure changes the scales and modify the
adaptive algorithm and the axis codes accordingly
2. Create a kwarg to tell plot() to implement the scale-change internally
3. Create other functions to use loglog(), semilogx() and semilogy()
4. Many (or all) of the above together, since they aren't mutually
exclusive
From what I noticed, Mathematica implements the separate functions way,
but it may be better to fix the issue in plot() itself and if the other
functions are wanted, just make it so that they call plot() with the
correct arguments
--
Comment:
I added a patch to `Graphics` class which introduces log plots. Some
salient points
1. I had to "disable" some tick formatting for log plots because
matplotlib wasn't behaving well with the formatting that is done in
`Graphics().maptplotlib()` (ex. the error in comment:11, out of memory
error, etc)
2. The patch in this ticket relies on the patches in #12974 which is
mostly a cleanup of the `Graphics` class.
3. In trying to implement my own class, I started to look at each of the
matplotlib functions more carefully, and found out the reason(s) why
setting the scale wasn't working (see point 1.). The result is that I
could implement log scale right inside `Graphics` by carefully weeding out
the corner cases. I hope I got all the corner cases.
Todo:
1. A patch to `plot()` and other functions will take more time to
implement. :(
2. Probably need to make sure that user does not specify tick formatters
and locators which don't behave well with log plots.
3. Feedback is welcome! I need to know if I missed something.
Example code:
{{{
p = plot(exp, 1, 10)
p.set_scale('loglog')
p.show()
xd=range(-5,5); yd=[10**_ for _ in xd]; p=list_plot(zip(xd,
yd),plotjoined=True)
p.set_yscale('log', 2) # Set only y-axis to log and with base of log being
2.
p.show()
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4529#comment:21>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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