Quotient ring can be created without generator names

[RalphieBoy]

The following code works:

sage: R.<x> = PolynomialRing(QQ)
sage: f = x^2-1
sage: S = R.quotient_by_principal_ideal(f)

but then this fails:

sage: S
 ---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
...[snip]
/Users/tmp/sage-3.4.alpha0/local/lib/python2.5/site-packages/sage/structure/category_object.so in sage.structure.category_object.CategoryObject.variable_names (sage/structure/category_object.c:3530)()

ValueError: variable names have not yet been set using self._assign_names(...)

The routine should require that the name(s) be provided.

Component: algebra

Author: Alex Ghitza

Reviewer: Mike Hansen

Merged: sage-4.3.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/5482

[RalphieBoy]

comment:1

Attachment: sage-5482.patch.gz

The fix is to require the generator name at creation time, not when the ring is used.

[JohnCremona]

comment:2

Why do you change the parameter name from "names" to "name"? Is this function only used for univariate polynomial rings? If so, fine.

[williamstein]

comment:4

REFEREE REPORT:

1. It must be "names" not "name", so the R. = foo notation works.

2. Every patch has to have a doctest that illustrates that it fixes the bug.

[RalphieBoy]

comment:5

Replying to @williamstein:

REFEREE REPORT:

1. It must be "names" not "name", so the R. = foo notation works.

I discovered that while adding doctests. I'll reverse that change.

2. Every patch has to have a doctest that illustrates that it fixes the bug.

Doctests?

[aghitza]

comment:7

I attached a new patch that assigns names automatically if they are not specified by the user, e.g. a quotient of R.<x> will have variable name xbar. This is standard behaviour in other places in Sage.

Apply trac_5482.patch only.

[aghitza]

Author: Alex Ghitza

[aghitza]

Attachment: trac_5482.patch.gz

apply this patch only

[mwhansen]

Reviewer: Mike Hansen

[mwhansen]

comment:8

Looks good to me.

[mwhansen]

Merged: sage-4.3.alpha0