Change log for Magma V2.13-15 (Released 24/8/2007)

Elliptic Curves

·The identity point on an elliptic curve over a p-adic field behaves somewhat better now. In particular, it is possible to coerce the coordinates of the identity point back into the curve.

·IsogenyFromKernelFactored applied to a group scheme now works (formerly triggered a runtime error).

·Fixed a bug in IsogenyFromKernel that would cause the resulting isogeny to be incorrect when the kernel contained the full two-torsion and the base field was not the rationals or a small finite field.

Hyperelliptic curves

·The map phi returned by TwoSelmerGroup was completely wrong in some cases, and has been corrected. (This problem was introduced in V2.13.) Reported by Patrick Corn.

Invariant Theory

·A bug in Module, when the secondaries were set via the attribute, has been fixed. Reported by D. Wehlau.

Lattices

·Problems lattice vector enumeration has been fixed (when the bound was close to the machine int size). Problem reported by Ronald van Luijk.

·A problem with the construction of sub-lattices of lattices with real valued gram matrices has been fixed. Without this, Magma would encounter internal errors.

Models of genus one curves

·A mistake in the HyperellipticCurve constructor has been corrected. Prior to this, for a model f(X) of degree 2 without cross-terms, HyperellipticCurve returned y2 = -f(x) instead of y2 = f(x). Reported by Bjorn Poonen.

Modules over Dedekind domains

·A bug in the handling and printing of parents of pseudo-matrices has been fixed. Without this fix, a sequence of pseudo matrices could cause internal errors. Bug reported by U. Staemmler.

Number Fields

·Several minor problems in the class group computation of number fields have been fixes. Together, they would trigger internal errors. Reported by N. Bruin.

·A bug in the unit group computation that, especially in fields with unit rank  â‰¥ 5 and small regulator could result in infinite loops, has been fixed. Bug reported by M. Kirschmer.

Polynomial Rings

·A bug in factorization of polynomials over function fields over quotient rings has been fixed. Reported by N. Bruin.

System

·Some bugs relating to interactions between integer factorization sequences (RngIntEltFact) and normal sequences (SeqEnum) have been fixed.