#13246: Automatic exclusion of non-domain points in things like arcsec
------------------------+---------------------------------------------------
Reporter: kcrisman | Owner: jason, was
Type: defect | Status: new
Priority: major | Milestone: sage-5.3
Component: graphics | Keywords:
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
------------------------+---------------------------------------------------
From an email exchange about plotting arcsec, slightly out of order:
The immediate context for this issue is a couple of problems that include,
among other things, graphing arcsec and its derivative (in one case),
arcsec and arccsc (in the other). Since the range of intended functions
is known, it appears that this would work if the students follow
instructions (big if). But more generally, we want students to have total
control over their "graphing calculator" -- at least over the input boxes
we provide -- so there's nothing stopping them from entering arcsec(x/2)
or something else that we can't anticipate.
The underlying problem is that the plotting code ignores everything
between -1 and 1 (since those values aren't real), but then simply
connects (-1,3) and (1,.2) (or so) with a line segment when it's done. I
have a couple ideas for fixing this, but they won't help you in the near
term.
----
One workaround for your @interact would be to select an option for
exclude based on the function: I'm thinking of something like this:
@interact
def foo(fn=textbox(), ....):
setup stuff...
if fn == 'arcsin':
exclude=[]
elif fn == 'arcsec':
exclude=[-1,1]
plot(fn, ...., exclude=exclude)
The idea is just to look at the function being plotted and set a list of
points to exclude based on that. It would be tedious to code, but would
work.
----
I think that fixing this is possible. I spent about a half hour looking
at http://hg.sagemath.org/sage-main/file/9ab4ab6e12d0/sage/plot/plot.py
just now and I am pretty sure that one could extract bad points like nan
in generate_plot_points. Currently we just do
data = [data[i] for i in range(len(data)) if i not in exception_indices]
which means we completely ignore them, but presumably we could keep this
data somehow and return it as part of generate_plot_points (not sure
whether that would have to be deprecated) so that we could add that
somehow to the exclude data around http://hg.sagemath.org/sage-
main/file/9ab4ab6e12d0/sage/plot/plot.py#l1279
The problem is that there could be a lot of these, and that could slow
things down a lot to check all of them, but checking for a "consecutive
series" would also take some time.
Anyway, it's at least doable in principle, but would take some time and
care to implement, making sure it didn't cause any other regressions.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13246>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/sage-trac?hl=en.
