Update pynac to 0.7.27 to fix wrong result on symbolic exponentiation #30446

dkrenn · 2020-08-26T14:33:36Z

Before this ticket:

sage: n((24*sqrt(3))^(100/50))
3.80392047155301e5927962146
sage: n((24*sqrt(3))^(2))
1728.00000000000

Clearly, both should be the same, namely the second.

This was on SageMath 9.1 on openSUSE Leap 15.2 (64bit) (reported by a colleague to me).

I've tried to reproduce, but my SageMath, as well as on CoCalc crashes. The error message on my machine was

Traceback (most recent call last):
  File "<string>", line 25, in <module>
ModuleNotFoundError: No module named 'Cython'
Error while executing Python code.
Saved trace to /home/dakrenn/.sage/crash_logs/crash_lqkqgydq.log
------------------------------------------------------------------------
Unhandled SIGABRT: An abort() occurred.
This probably occurred because a *compiled* module has a bug
in it and is not properly wrapped with sig_on(), sig_off().
Python will now terminate.
------------------------------------------------------------------------
Aborted (core dumped)

However, my SageMath seems to be fine otherwise, make ptestlong passes.
Same on current 9.2.beta9.

Depends on #31118

Upstream: None of the above - read trac for reasoning.

CC: @zimmermann6

Component: symbolics

Author: Ben Livingston, Dima Pasechnik

Branch: ccdf77c

Reviewer: Dima Pasechnik, Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/30446

The text was updated successfully, but these errors were encountered:

DaveWitteMorris · 2020-08-26T16:35:48Z

comment:1

I confirm the error. I get exactly the same answers as in the original report. I am using Mac OS 10.15.5, and tested both 9.1 and 9.2b10. (The version with 100/2 is slow -- takes about 50 seconds.)

When I tried CoCalc, it failed because it ran out of memory. (The memory gauge was over 3GB before it aborted.)

DaveWitteMorris · 2020-10-01T04:18:00Z

comment:3

There is no need to use big numbers, so the situation is even worse than it first appeared:

sage: n((2*sqrt(2))^(2/1))                                                      
1.24131221754531e1292913987
sage: n((2*sqrt(2))^2)                                                          
8.00000000000000

This only takes a few seconds with 9.1 on CoCalc (but needs more than 1GB of memory) or with 9.2b13 on MacOS 10.15.6.

mantepse · 2020-10-01T08:01:26Z

comment:4

I can confirm this on Ubuntu 18 with SageMath version 9.2.beta13, using Python 3.8.5.

bmlivin · 2020-10-03T23:17:23Z

comment:5

Okay, I believe I've tracked this down. It is a pynac bug. Here's what's happening:

Sage eventually calls pynac's pow from sage.symbolic.expression:Expression._pow_, but before that happens, it simplifies the exponent. Specifically, it simplifies the exponent so that pynac thinks it is an integer, but its type is still MPQ.

None of that should matter, except that what pynac calls to evaluate the expression is numeric::pow_intexp. Here is the content of that function:

if (not exponent.is_integer())
    throw std::runtime_error("nueric::pow_intexp: exponent not integer");
if (exponent.t == MPZ) {
    if (not mpz_fits_sint_p(exponent.v._bigint))
        throw std::runtime_error("size of exponent exceeds signed long size");
    return power(mpz_get_si(exponent.v._bigint));
}
return power(exponent.v._long);

In this function, exponent.is_integer() is True and exponent.t is MPQ. So both of the if statements are false, and power(exponent.v._long) is called. The problem is that v._long contains junk (very large junk!). Evaluating that statement takes a long time, and it won't give you the answer you want.

If, on the other hand, the second if statement were true, the result would have been exactly what you want. So simply checking whether exponent.t == MPQ or exponent.t == MPZ should fix this. I haven't tried this, but it's what I would at least try.

I think it may be possible as well to fix this by getting Sage to change the type of the exponent when it's cancelled out. I haven't looked into this and I think it sounds like a bad idea.

I'm unassigning this because I can't currently report it upstream.

bmlivin · 2020-10-03T23:17:23Z

Upstream: Not yet reported upstream; Will do shortly.

bmlivin · 2020-10-12T02:29:53Z

Author: Ben Livingston

bmlivin · 2020-10-12T02:29:53Z

Changed upstream from Not yet reported upstream; Will do shortly. to Fixed upstream, in a later stable release.

bmlivin · 2020-10-12T02:29:53Z

comment:6

I've fixed this upstream and submitted a pull request: pynac/pynac#355. The pull request also includes additions to the doctest for sage.symbolic.expression.Expression::_pow_.

dimpase · 2021-01-10T11:51:46Z

comment:8

OK, trying https://patch-diff.githubusercontent.com/raw/pynac/pynac/pull/355.patch now.

But where are "additions to the doctest for sage.symbolic.expression.Expression::_pow_"?

I presume they should be here, on this ticket.

dimpase · 2021-01-10T11:59:04Z

comment:9

OK, with that patch,

sage: QQ((24*sqrt(3))^(100/50))==1728                                                                                                                                
True

works. I'll add this as a doctest somewhere.

dimpase · 2021-01-10T12:37:55Z

Branch: u/dimpase/packages/pynac/30446

dimpase · 2021-01-10T12:37:55Z

Reviewer: Dima Pasechnik

dimpase · 2021-01-10T12:37:55Z

Commit: dc073df

dimpase · 2021-01-10T12:37:55Z

comment:10

patches from pynac PRs to be removed at the next pynac update.

New commits:

`dc073df`	`fixes for trac #30446`

DaveWitteMorris · 2021-01-10T22:43:55Z

comment:11

This patch to pynac also fixes #28620, #30304, and #30786. The PR at #30786 adds doctests for all 3 of these tickets (and also moves the doctest of this ticket from the _latex_ method to the _pow_ method, which seems like a more appropriate place).

DaveWitteMorris · 2021-01-11T02:05:23Z

comment:12

fyi: Patchbot Linux/74-Ubuntu_SMP_Tue_Sep_17_17%3A06%3A04_UTC_2019/x86_64/4.15.0-65-generic/pc72 seems to have failed to build pynac at ticket #30786. ("Error installing package pynac-0.7.26.sage-2020-04-03.p1") If there is a genuine problem, I think it must be because of this ticket.

DaveWitteMorris · 2021-01-12T02:26:51Z

comment:13

This patch also seems to fix #31137. I added a doctest there.

DaveWitteMorris · 2021-01-12T08:21:58Z

comment:14

fyi: Another ubuntu patchbot failed to build pynac (on ticket #31137 this time). Both failures say WARNING: 'aclocal-1.16' is missing on your system. ... Makefile:432: recipe for target 'aclocal.m4' failed.

vbraun · 2021-01-17T19:26:38Z

comment:15

Patch touches configure stuff which triggers automake run (which is not a Sage dependency)

Building pynac-0.7.26.sage-2020-04-03.p1
CDPATH="${ZSH_VERSION+.}:" && cd . && /bin/bash /var/lib/buildbot/slave/sage_git/build/local/var/tmp/sage/build/pynac-0.7.26.sage-2020-04-03.p1/src/missing aclocal-1.16 -I m4
/var/lib/buildbot/slave/sage_git/build/local/var/tmp/sage/build/pynac-0.7.26.sage-2020-04-03.p1/src/missing: line 81: aclocal-1.16: command not found
WARNING: 'aclocal-1.16' is missing on your system.
         You should only need it if you modified 'acinclude.m4' or
         'configure.ac' or m4 files included by 'configure.ac'.
         The 'aclocal' program is part of the GNU Automake package:
         <https://www.gnu.org/software/automake>
         It also requires GNU Autoconf, GNU m4 and Perl in order to run:
         <https://www.gnu.org/software/autoconf>
         <https://www.gnu.org/software/m4/>
         <https://www.perl.org/>
Makefile:432: recipe for target 'aclocal.m4' failed
make[5]: *** [aclocal.m4] Error 127
make[5]: Failed to remake makefile 'Makefile'.
make[5]: Target 'all' not remade because of errors.

mkoeppe · 2021-01-24T21:56:36Z

comment:29

build/pkgs/pynac/SPKG.rst could use an update. In particular "Special Update/Build Instructions" should be removed

mkoeppe · 2021-01-24T21:57:11Z

Changed reviewer from Dima Pasechnik to Dima Pasechnik, Matthias Koeppe

sagetrac-git · 2021-01-24T22:07:25Z

Changed commit from 214712d to ccdf77c

sagetrac-git · 2021-01-24T22:07:25Z

Branch pushed to git repo; I updated commit sha1 and set ticket back to needs_review. New commits:

`ccdf77c`	`update SPKG.rst`

dimpase · 2021-01-24T22:08:07Z

comment:34

ok, done

vbraun · 2021-02-08T00:10:03Z

comment:36

[dochtml] [calculus ] docstring of sage.symbolic.expression.Expression.subs:135: WARNING: Literal block expected; none found.
[dochtml] [calculus ] docstring of sage.symbolic.expression.Expression.substitute:135: WARNING: Literal block expected; none found.
[dochtml] [manifolds] The inventory files are in local/share/doc/sage/inventory/en/reference/manifolds.
[dochtml] Build finished. The built documents can be found in /home/release/Sage/local/share/doc/sage/inventory/en/reference/manifolds
[dochtml] [calculus ] The inventory files are in local/share/doc/sage/inventory/en/reference/calculus.
[dochtml] Error building the documentation.
[dochtml] Traceback (most recent call last):
[dochtml]   File "/usr/lib64/python3.9/runpy.py", line 197, in _run_module_as_main
[dochtml]     return _run_code(code, main_globals, None,
[dochtml]   File "/usr/lib64/python3.9/runpy.py", line 87, in _run_code
[dochtml]     exec(code, run_globals)
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/__main__.py", line 2, in <module>
[dochtml]     main()
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/__init__.py", line 1730, in main
[dochtml]     builder()
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/__init__.py", line 343, in _wrapper
[dochtml]     getattr(get_builder(document), 'inventory')(*args, **kwds)
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/__init__.py", line 569, in _wrapper
[dochtml]     self._build_everything_except_bibliography(lang, format, *args, **kwds)
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/__init__.py", line 555, in _build_everything_except_bibliography
[dochtml]     build_many(build_ref_doc, non_references)
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/__init__.py", line 295, in build_many
[dochtml]     _build_many(target, args, processes=NUM_THREADS)
[dochtml]   File "/home/release/Sage/local/lib64/python3.9/site-packages/sage_setup/docbuild/utils.py", line 289, in build_many
[dochtml]     raise worker_exc.original_exception
[dochtml] OSError: docstring of sage.symbolic.expression.Expression.subs:135: WARNING: Literal block expected; none found.
[dochtml] 
[dochtml]     Note: incremental documentation builds sometimes cause spurious
[dochtml]     error messages. To be certain that these are real errors, run
[dochtml]     "make doc-clean" first and try again.

mkoeppe · 2021-02-20T16:55:34Z

comment:37

Could someone fix up the documentation markup please?

DaveWitteMorris · 2021-02-21T20:27:40Z

comment:38

I can't find any mistake, the patchbots are green, and the html documentation builds for me.

I wonder if maybe this error was posted to the wrong ticket? It is exactly the same error that was reported by a patchbot on ticket #30378 because I goofed up the WARNING block there:

[dochtml] OSError: docstring of sage.symbolic.expression.Expression.subs:135: WARNING: Literal block expected; none found.

mkoeppe · 2021-02-21T21:12:40Z

comment:39

Thanks for checking! Works for me too (tested on top of 31344)

vbraun · 2021-03-07T17:06:32Z

Changed branch from u/dimpase/packages/pynac/0727 to ccdf77c

slel · 2021-03-07T18:25:58Z

Changed commit from ccdf77c to none

dkrenn added this to the sage-9.2 milestone Aug 26, 2020

dkrenn added c: symbolics labels Aug 26, 2020

bmlivin mannequin self-assigned this Sep 21, 2020

bmlivin mannequin removed their assignment Oct 3, 2020

bmlivin mannequin added the s: needs review label Oct 12, 2020

mkoeppe modified the milestones: sage-9.2, sage-9.3 Oct 24, 2020

dimpase added s: positive review and removed s: needs review labels Jan 10, 2021

mkoeppe added s: positive review and removed s: needs review labels Jan 24, 2021

mkoeppe changed the title ~~wrong result on symbolic exponentiation~~ Update pynac to 0.7.27 to fix wrong result on symbolic exponentiation Jan 24, 2021

sagetrac-git mannequin added s: needs review and removed s: positive review labels Jan 24, 2021

dimpase added s: positive review and removed s: needs review labels Jan 24, 2021

vbraun added s: needs work and removed s: positive review labels Feb 8, 2021

mkoeppe added s: positive review and removed s: needs work labels Feb 21, 2021

vbraun removed the s: positive review label Mar 7, 2021

vbraun closed this as completed in 61c5e09 Mar 7, 2021

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EmmanuelCharpentier mannequin mentioned this issue Jan 12, 2021

Sage fails to compute a (simple) symbolic expression #28620

Closed

zimmermann6 mentioned this issue Jan 29, 2023

runtime error with simple expression #29156

Open

EmmanuelCharpentier mannequin mentioned this issue Mar 7, 2021

Crash when expanding square root of -x #30688

Closed

GMS103 mentioned this issue Mar 9, 2021

Multiplying and dividing by 3 hangs #30786

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EmmanuelCharpentier mannequin mentioned this issue Mar 9, 2021

Fix subs failure involving integer-valued rational exponents #31137

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Update pynac to 0.7.27 to fix wrong result on symbolic exponentiation #30446

Update pynac to 0.7.27 to fix wrong result on symbolic exponentiation #30446

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Update pynac to 0.7.27 to fix wrong result on symbolic exponentiation #30446

Update pynac to 0.7.27 to fix wrong result on symbolic exponentiation #30446

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