Multiplying and dividing by 3 hangs

[GMS103]

Tested with https://sagecell.sagemath.org

sage: version()
'SageMath version 9.1, Release Date: 2020-05-20'

All of these work as expected:

sage: exp(-ln(-x))
sage: exp(-3*ln(-x)/3)
sage: exp(-ln(-9*x))

However this hangs:

sage: exp(-3*ln(-9*x)/3)

In case you are curious, this is what I was doing (the expressions were a bit more complex, of course):

sage: a=var('a')
sage: y=exp(-3*x)
sage: x0=ln(-9*a)/3
sage: y(x=x0)

Depends on #30446

Component: symbolics

Author: Dave Morris

Branch/Commit: 6ee3113

Reviewer: Travis Scrimshaw, Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/30786

[DaveWitteMorris]

comment:1

I confirm that there is a problem. CoCalc ran out of memory. My laptop (9.2rc2 on MacOS 10.15.7) completed eventually (I think it took about half an hour). The output is a 4GB string of nonsense that seems to be almost entirely digits, but starts with -1/34723950083 and ends with 91987451449/x.

These symptoms are somewhat similar to #30446.

[bmlivin]

comment:2

DaveWitteMorris is correct. I checked and this is the same issue as #30446. If you look on that ticket, I submitted a pull request with pynac that will fix the issue.

[GMS103]

comment:3

Thanks for the feedback, I was really surprised by this bug.
Glad to know it will be fixed.

[DaveWitteMorris]

comment:4

As pointed out in comment:2, this will be fixed by the patch to pynac in #30446. When that ticket is closed, we can add this as another doctest.

[DaveWitteMorris]

Dependencies: #30446

[DaveWitteMorris]

Branch: public/30786

[DaveWitteMorris]

comment:6

The PR adds doctests for the bugs on this ticket, #28620, and #30304. All were fixed by the patch to pynac at #30446 (which has positive review). These doctests are in the _pow_ method, and I moved the doctest of #30446 to the same place. (It was in the _latex_ method, which does not seem like such a good place.)

---

New commits:

dc073df	fixes for trac #30446
4a5d053	doctests for trac 28620, 30304, 30786

[DaveWitteMorris]

Commit: 4a5d053

[DaveWitteMorris]

Author: Dave Morris

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:7

LGTM.

[DaveWitteMorris]

comment:8

Thanks!

[dimpase]

comment:9

rebase over new #30446

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

9d747fc	sage --package update-latest: Distinguish pypi package name and spkg name
f74f66c	sage --package update-latest: Accept package classes :standard:, :optional: etc., restrict to normal Python packages
182b3d2	sage -package fix-checksum: Handle package classes, ignore non-normal packages
9a57cf6	pynac update
563940e	doctest from #30446
51def3c	sane version name
4834dc8	remove upstreamed patch
214712d	tarball update
6ee3113	doctests for trac 28620, 30304, 30786

[sagetrac-git]

Changed commit from 4a5d053 to 6ee3113

[dimpase]

Changed reviewer from Travis Scrimshaw to Travis Scrimshaw, Dima Pasechnik

[dimpase]

comment:11

OK, done

[vbraun]

Changed branch from public/30786 to 6ee3113