Change log for Magma V2.16-10 (Released 28/5/2010)

AlgebraicCurves

·A bug in the construction of places from points has been fixed. This was causing crashs/errors in multiple curve functions relating to places and divisors. Examples in Pushforward, Valuation, Decomposition and DifferentialSpace were reported by Michael Stoll and Nils Bruin. These have all been solved by the fix.

·Pushforward of places by a map has been modified so that it should now work even if the map is not defined at the conjugate set of points that it lies over.

·Intrinsic IsHypersurfaceDivisor added, that computes whether an effective divisor on an ordinary projective curve is given by the scheme-theoretic intersection with a hypersurface and returns such a hypersurface in the affirmative case.

Coding Theory

·Improvement to the handling of IsProjective for linear codes, and the addition of IsProjective and IsAdditiveProjective for additive codes.

·Fixed a bug in the minimum weight computation of quantum codes when using the Zimmermann algorithm. Also fixed the verbose output which was incorrectly listing some words as impurities which were not. Reported by M. Grassl.

Elliptic Curves

·A minor printing problem with variables in TwoDescent was fixed.

·A fix involving TwoDescent of elliptic curves over Q was made to ensure that enough precision was used in local completion. Bug reported by Edray Goins.

FP Groups

·SimpleQuotients has been modified to make each signature consistent in behaviour. One signature which took a tuple as argument has been removed; the others now have a consistent set of parameters Limit, HomLimit, and Family.

·Important: The parameter GroupLimit was renamed to Limit, and the parameters LowDegree and HighDegree have been removed. Any existing code using these parameters needs to be adjusted, by renaming the parameter in the first instance, and by calling the corresponding signature that takes degree ranges in the second. Also, the default for Limit is 1, whereas the default for GroupLimit used to be 0.

Global Arithmetic Fields

·The computation of residue fields in orders having a multiply relative representation has been fixed.

·A problem related to the numbering of the generators for number fields has been fixed. This could have caused internal errors using GeneratorsSequence for affected fields.

Local Arithmetic Fields

·The powering algorithm for power series rings over local rings has been changed to a slower, but more numerically stable method. Reported by E. Thome.

·The algorithm to compute the group of 1-units in a p-adic local ring suffered from strange precision loss resulting in non-sensical answers. Reported by N. Bruin.

·An algorithm to compute the unit group (multiplicative group) of fixed precision p-adic quotients has been provided.

·Factorization of inseparable polynomials over series rings has been fixed. Reported by R. Butenuth.

Mappings

·Homomorphisms between abelian groups can now be tested for being surjective. Reported by J. Walker.

Matrices

·The sequence of returned matrices from Minors is more consistently sorted now. Bug reported by G. Macario-Rat.

Matrix Groups

·Two bugs in the standard forms code for classical groups have been fixed. Bugs reported by Derek Holt. Eamonn O'Brien was also involved in noticing them.

·Major improvements have been made to the algorithm for proving a matrix group over a ring of characteristic zero to be finite or infinite (in particular, in the function IsFinite).

Schemes

·The application of maps between elliptic curves to ring elements (specifically 0) will treat the input as an element of the coordinate ring of the ambient of the domain if possible.

Simple Groups Database

·A bug in SimRecordRequire from the simgps database has been fixed. Reported by M. Conder.