symbolic integration fails on a very simple test case

[pdehaye]

The following happens

sage: var("x")
x
sage: integrate(abs(x - 1) + abs(x + 1) - 2*abs(x), (x,-Infinity,Infinity))
0
sage: integrate(abs(x - 1) + abs(x + 1) - 2*abs(x),(x,-Infinity,10))
2

The second answer is the correct one, of course...

Upstream: Fixed upstream, in a later stable release.

CC: @kcrisman

Component: calculus

Keywords: integrate

Author: Michael Orlitzky

Reviewer: Karl-Dieter Crisman

Merged: sage-5.0.beta11

Issue created by migration from https://trac.sagemath.org/ticket/11445

[kcrisman]

comment:1

This also happens in Maxima.

Maxima 5.24.0 http://maxima.sourceforge.net
using Lisp SBCL 1.0.24
Distributed under the GNU Public License. See the file COPYING.
Dedicated to the memory of William Schelter.
The function bug_report() provides bug reporting information.
(%i1) integrate(abs(x - 1) + abs(x + 1) - 2*abs(x),x,minf,10);
(%o1)                                  2
(%i2) integrate(abs(x - 1) + abs(x + 1) - 2*abs(x),x,minf,inf);
(%o2)                                  0

I don't know that I would call this "very simple", though, as integrating absolute value things is somewhat tricky when done symbolically.

[kcrisman]

Upstream: Not yet reported upstream; Will do shortly.

[pdehaye]

comment:2

sure, but certainly something i would hope works! also not sure how much of it is due to the infinite interval and how much due to the function itself

[kcrisman]

comment:3

This is now reported at this location.

[kcrisman]

Changed upstream from Not yet reported upstream; Will do shortly. to Reported upstream. Little or no feedback.

[pdehaye]

comment:4

fixed over there

[pdehaye]

Changed upstream from Reported upstream. Little or no feedback. to Fixed upstream, in a later stable release.

[orlitzky]

Doctest for the correct result.

[orlitzky]

Author: Michael Orlitzky

[orlitzky]

comment:7

Attachment: sage-trac_11445.patch.gz

Fixed now that we've got Maxima 5.26.0. Here's a doctest.

[kcrisman]

Reviewer: Karl-Dieter Crisman

[kcrisman]

comment:8

I probably would have put it in sage.symbolic.integration.integral.integral somewhere, where there are lots of tests, but I guess this is fine, and otherwise all is well. I'd hate to have you rebase it to that other location, seems a waste... but then again, that's where they are...

Or what do you think? The problem is that we have no canonical location for integral stuff. integrate? is a wasteland, though it points to better sources of doc.

[orlitzky]

comment:9

I honestly went through the same thought process. At first, I thought, "I'll put it with the Maxima stuff because it was a Maxima bug." But then I thought, what if we ever drop Maxima completely? This isn't a Maxima test: this tests that our integration works. Whatever we would replace Maxima with should also pass this test!

Then, I had to decide whether to put it in functional.py or under symbolics. I settled on this because it's what gets called first when the user calls integrate(). It's also where you're sent if you look up the code with integrate? or integrate??, so to stay true to the report on the ticket, I put it there.

If the reporter had done,

f = abs(x - 1) + abs(x + 1) - 2*abs(x)
f.integral(...)

I probably would have stuck it in symbolics. It's no big deal to move it, in any case.

[kcrisman]

comment:10

Well, you'll notice that I did give positive review. You are right about the integration tests not belonging in the Maxima docs, of course.

[jdemeyer]

Merged: sage-5.0.beta11