Doctests: Even reals are integers

[pelegm]

Check this:

sage: assume(x, 'even')
sage: assume(x, 'real')
sage: simplify((-1)**x)
1
sage: x.is_integer()
False

At least for real numbers (or even for complex numbers), an even number should be assumed to be an integer.

This is how it works in SymPy:

In [2]: x = Symbol('x', even=True)

In [3]: x.is_integer
Out[3]: True

Was supposed to be fixed in pynac-0.7.4. This will also work and should be doctested here:

sage: sage: assume(x, 'even')
....: sage: assume(x, 'real')
....: 
sage: (-1)^x
1
sage: (-gamma(pi))^x
gamma(pi)^x

Depends on #22219

Component: symbolics

Keywords: is_integer, assume

Author: Ralf Stephan

Branch/Commit: 81e3fba

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/22026

[pelegm]

comment:1

I wasn't sure if I should report this as a defect or as an enhancement.

I'll add that if one tries

sage: assume(x, 'noninteger')

an error is raised:

Traceback (most recent call last):
...
ValueError: Assumption is inconsistent

so "someone" knows x is an integer...

[rwst]

comment:2

Yes, Maxima knows. The inference logic however is in Pynac.

[rwst]

Upstream: Reported upstream. Developers acknowledge bug.

[rwst]

comment:3

This is now pynac/pynac#225

[rwst]

Dependencies: pynac-0.7.4

[rwst]

Changed upstream from Reported upstream. Developers acknowledge bug. to Fixed upstream, but not in a stable release.

[rwst]

comment:6

Not fixed in Pynac, huh.

[rwst]

comment:7

Issue is fixed. Only doctests needed.

[rwst]

Branch: u/rws/doctests__even_reals_are_integers

[rwst]

Author: Ralf Stephan

[rwst]

Commit: 81e3fba

[rwst]

New commits:

81e3fba

22026: Doctest: Even reals are integer

[rwst]

Changed dependencies from pynac-0.7.4 to #22219

[rwst]

Changed upstream from Fixed upstream, but not in a stable release. to none

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:10

LGTM.

[vbraun]

Changed branch from u/rws/doctests__even_reals_are_integers to 81e3fba