Disallow mixing of pos.char.ring elements and symbolic variables

[rwst]

This is to have a place for code examples and discussion of impact of the proposal in https://groups.google.com/forum/?hl=en#!topic/sage-devel/auLwQWtpnz0

The following produces a segmentation fault (Sage 7.4, Ubuntu 14.04 or OS X 10.10.5),
see Ask Sage.

sage: F = GF(3)
sage: num, den = F(2)*x + F(1), x
sage: num/den
 ... segmentation fault ...

With this branch this gives: TypeError: Multiplication of symbolic variable and an element of a ring with positive characteristic.

See also sage-support.

CC: @jdemeyer @videlec @slel

Component: symbolics

Keywords: segfault

Branch/Commit: u/rws/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables @ 8de8398

Reviewer: Ralf Stephan

Issue created by migration from https://trac.sagemath.org/ticket/21391

[rwst]

Branch: u/rws/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables

[rwst]

comment:2

In a first scan these doctests would have to be changed:

sage -t src/sage/symbolic/expression.pyx  # 11 doctests failed
sage -t src/sage/symbolic/pynac.pyx  # 2 doctests failed
sage -t src/sage/rings/polynomial/polynomial_element.pyx  # 2 doctests failed
sage -t src/sage/rings/polynomial/laurent_polynomial.pyx  # 2 doctests failed
sage -t src/sage/rings/polynomial/polynomial_zz_pex.pyx  # 1 doctest failed

---

New commits:

7147699

21391: Disallow mixing of pos.char.ring elements and symbolic variables

[rwst]

Commit: 7147699

[rwst]

Author: Ralf Stephan

[rwst]

comment:3

Alternatively this could be made a stopgap. Which is better?

[slel]

Changed keywords from none to segfault

[slel]

comment:4

Adding an example leading to a segmentation fault to the ticket description.

[sagetrac-git]

Changed commit from 7147699 to f2933cc

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

dd6ad96	Merge branch 'develop' into t/21391/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables
03ccd07	Merge branch 'develop' into t/21391/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables
f2933cc	21391: introduce ex.has_finite_parent()

[rwst]

comment:9

Critical because of segfault and public interest.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

333db3c

Merge branch 'develop' into t/21391/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables

[sagetrac-git]

Changed commit from f2933cc to 333db3c

[rwst]

comment:11

Doctest failures.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

8700e00	Merge branch 'develop' into t/21391/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables
c7f8ad2	21391: to prevent fails give the coordinate functions an explicit characteristic
9430605	21391: doctest fixes

[sagetrac-git]

Changed commit from 333db3c to 9430605

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

8de8398

Merge branch 'develop' into t/21391/disallow_mixing_of_pos_char_ring_elements_and_symbolic_variables

[sagetrac-git]

Changed commit from 9430605 to 8de8398

[rwst]

comment:15

Doctest failures.

[koffie]

comment:16

I think this can be closed as duplicate since #24072 has positive review.

[jdemeyer]

Changed author from Ralf Stephan to none

[jdemeyer]

Reviewer: Ralf Stephan