not all fractions get converted with ex.fraction()

[rwst]

sage: a = var('a')
sage: b = (1/a).fraction(QQ)
...
TypeError: unsupported operand parent(s) for '/': 'Univariate Polynomial Ring in x over Rational Field' and 'Univariate Polynomial Ring in a over Rational Field'

The 1 apparently gets coerced into the x-ring, so we need to ensure equal rings somehow.

Component: symbolics

Author: Ralf Stephan

Branch/Commit: b46d1df

Reviewer: Martin Albrecht

Issue created by migration from https://trac.sagemath.org/ticket/17736

[rwst]

Branch: u/rws/not_all_fractions_get_converted_with_ex_fraction__

[rwst]

Commit: b46d1df

[rwst]

New commits:

b46d1df

17736: not all fractions get converted with ex.fraction()

[rwst]

Author: Ralf Stephan

[rwst]

comment:3

Passes all patchbot tests.

[malb]

Reviewer: Martin Albrecht

[malb]

comment:4

Looks good to me. A potential feature request could be to allow the user to specify the ordering of variables, but perhaps that's overkill?

[rwst]

comment:5

I'm not so familiar with algebra. Would you suggest specific orderings or is there a convention?

[malb]

comment:6

Hi, sorry for not being clear:

I merely meant the ordering of variable (names), where you currently call sort(). But as I said: it's an optional feature request which could go into a separate ticket.

Of course, arbitrary term ordering ("lex" and "deglex" etc.) could also be considered. But I'd say a user should do the conversion by hand perhaps in this case.

[rwst]

comment:7

Replying to @malb:

I merely meant the ordering of variable (names), where you currently call sort(). But as I said: it's an optional feature request which could go into a separate ticket.

Ah but yes, I agree. Thanks for the review.

[vbraun]

Changed branch from u/rws/not_all_fractions_get_converted_with_ex_fraction__ to b46d1df