Title: Change log for Magma V2.17-11
Author: Computational Algebra Group

Change log for Magma V2.17-11 (Released 5/9/2011)

Algebraic Function Fields

•A crash in multiplication of ideals of non-simple relative orders has been fixed. Reported by V. Ducet.

•A crash in denominator handling of elements of non-simple relative orders has been fixed. Reported by V. Ducet.

•Computing an expansion at a prime of an element of a non-simple field has been fixed.

•IsSimple has been fixed for Function fields.

•Multivariate factorization and primary decomposition over non-simple function fields has been improved.

•Handling of linear extensions has been improved in RationalExtensionRepresentation of a tower of linear extensions.

Algebraic Number Fields

•Ensure that IsSubfield always installs an embedding when returning true, there was one missing between cyclotomic fields.

Basic Algebras

•An obscure crash involving basic algebras has been fixed. Reported by J. Carlson.

Coding Theory

•Fixed a bug in the minimum weight determination of quantum codes; this bug was introduced in V2.16, and could cause some words of low weight to be incorrectly ignored as impurities. Reported by M. Grassl and N. Aydin.

Coxeter Groups

•A crash in GrowthFunction for finitely presented Coxeter groups has been fixed. Crash found by an unknown user of the online calculator.

Elliptic Curves

•A bug with local heights of torsion points (involving infinite valuations) was fixed.

•A bug with local heights at infinity when the discriminant was negative was fixed.

•Trivial runtime errors in EllipticCurve(C) (where C is a curve) has been fixed.

Global Arithmetic Fields

•A problem in multiplication of ideals of relative orders has been fixed.

•Checking whether elements are in ideals of non-simple relative orders has been fixed. Reported by V. Ducet.

•Computing a 2 element representation of an ideal when the 1st generator is 1 has been fixed.

•Computing a 2 element representation of a fractional ideal has been fixed.

Groups

•The amount of set-up time for Random applied to a high degree matrix group has been reduced on the advice of E. O'Brien.

•The selection of base points in RandomSchreier for matrix groups has been fixed to use the equivalent of the GoodBasePoints function. Problem reported by E. O'Brien.

•The algorithm for subgroups of pc-groups where there is a low index limit has been improved to eliminate more cases more quickly.

•A case where AbelianQuotient applied to an fp-group failed to return a map has been fixed. Bug reported by S. Humphries.

•A crash in LowIndexSubgroups applied to a permutation group has been fixed. The crash was a memory management issue, and the fix may improve the general reliability of the system.

Hyperelliptic Curves

•Problems with type-checking in RationalPoint have been fixed. (Reported by Nils Bruin.)

Lie Theory

•Argument checking for GroupOfLieType has been improved.

Polytopes

•Added the optional database of l-reflexive polygons up to index 200. This can be accessed via PolytopelReflexiveDim2.

•The new WritePolytopeToPSFile intrinsic can be used to output a polygon to a PostScript file.

•The signature of Width has changed. The algorithm has been adjusted to make use of LLL, and now gives (as the second return value) the set of all primitive forms that yield the minimum width.

Quaternion Algebras

•OptimizedRepresentation of a quaternion algebra or an order of has been fixed.

System

•Fixed a bug where Read(F, n) would always return strings with internal length set to n, even if end-of-file was encountered. This function also now returns EOF when appropriate. Reported by A. Kasprzyk.