Elliptic curve constructor does not check if the base is a field properly

[JohnCremona]

Example:

sage: E = EllipticCurve(QQbar,[1,0])
sage: E.base_field()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)

/home/jec/sage/isog50.py in <module>()

AttributeError: 'EllipticCurve_generic' object has no attribute 'base_field'

This is because the curve constructed is an ell_generic and not an ell_field, despite {{{QQbar.is_field()}} returning True.

Similarly with RR and CC in place of QQbar.

All that is required is a two-line addition around line 213 of elliptic_curves/constructor.py.

Patch up soon.

CC: @sagetrac-JCooley

Component: elliptic curves

Author: John Cremona

Reviewer: Mike Hansen

Merged: Sage 4.1.2.alpha4

Issue created by migration from https://trac.sagemath.org/ticket/6879

[JohnCremona]

Attachment: trac_6879-ell_field.patch.gz

Applies to 4.1.1

[JohnCremona]

comment:1

Patched applies to 4.1.1. All sage/schemes/elliptic_curves tests ok.

[JohnCremona]

Author: John Cremona

[mwhansen]

Reviewer: Mike Hansen

[mwhansen]

comment:3

Looks good to me.

[sagetrac-mvngu]

Merged: Sage 4.1.2.alpha3

[sagetrac-mvngu]

comment:5

There is no 4.1.2.alpha3. Sage 4.1.2.alpha3 was William Stein's release for working on making the notebook a standalone package.

[sagetrac-mvngu]

Changed merged from Sage 4.1.2.alpha3 to Sage 4.1.2.alpha4