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GAP 4.4 Update 8 (September 2006)

New or improved functionality

  1. A function Positions with underlying operation PositionsOp, which returns the list of all positions at which a given object appears in a given list.
  2. LogFFE now returns fail when the element is not a power of the base.
  3. It is now allowed to continue long integers, strings or identifiers by ending a line with a backslash or with a backslash and carriage return character. So, files with GAP code and DOS/Windows-style line breaks are now valid input on all architectures.
  4. The command line for starting the session and the system environment are now available in GAPInfo.SystemCommandLine and GAPInfo.SystemEnvironment.
  5. Names of all bound global variables and all component names are available on GAP level.
  6. Added a few new Conway polynomials computed by Kate Minola and John Bray.
  7. There is a new concept of random sources, see IsRandomSource, which provides random number generators which are independent of each other.

    There is kernel code for the Mersenne twister random number generator (based on the code by Makoto Matsumoto distributed here). It provides fast 32 bit pseudo random integers with a period of length 2^19937-1 and a 623-dimensional equidistribution. The library methods for random elements of lists and for random (long) integers (Random(low, high)) are using the Mersenne twister now.

  8. In line editing mode (usual input mode without -n option) in lines starting with gap> , > or brk> this beginning part is immediately removed. This is a convenient feature that allows one to cut and paste input lines from other sessions or from manual examples into the current session.

Fixed bugs which could produce wrong results

  1. The function Decomposition returned coefficient vectors also in certain situations where in fact no decomposition exists. This happened only if the matrix entered as the first argument contained irrational values and a row in the matrix entered as the second argument did not respect the algebraic conjugacy relations between the columns of the first argument. So there was no problem for the usual cases that the two matrices are integral or that they are lists of Brauer characters. [Reported by Jürgen Müller]
  2. PC group homomorphisms can claim a wrong kernel after composition. [Reported by Serge Bouc]
  3. The return value of OctaveAlgebra had an inconsistent defining structure constants table for the case of coefficients fields not containing the integer zero. [Reported by Gábor Nagy]
  4. The manual guarantees that a conjugator automorphism has a conjugating element in the group if possible. This was not guaranteed.
  5. StabChain for symmetric groups gave a wrong result if fixed points were prescribed for base.
  6. Contrary to what is documented the function POW_OBJ_INT returned an immutable result for POW_OBJ_INT(m,1) for a mutable object m. This is triggered by the code m^1.
  7. PseudoRandom for a group had a problem if the group had lots of equal generators. The produced elements were extremely poorly distributed in that case. This is now fixed for the case that elements of the group can easily be sorted.
  8. Fixed the bug that the type of a blist was computed wrongly: The type previously had IS_PLIST_REP instead of IS_BLIST_REP in its filter list.
  9. Orbits did not respect a special PositionCanonical method for right transversals. [Reported by Steve Costenoble]
  10. Wrong results for GcdInt for some arguments on 64 bit systems only. [Reported by Robert Morse]
  11. When prescribing a subgroup to be included, the low index algorithm for fp groups sometimes returned subgroups which are in fact conjugate. (No subgroups are missing.) [Reported by Ignaz Soroko]

Fixed bugs which could lead to crashes

  1. The command line option -x allowed arguments > 256 which can then result in internal buffers overflowing. Now bigger numbers in the argument are equivalent to -x 256. [Reported by Michael Hartley]

Other fixed bugs

  1. Two special methods for the operation CompositionMapping2 were not correct, such that composing (and multiplying) certain group homomorphisms did not work. [Reported by Peter Mayr]
  2. In the definition of FrobeniusCharacterValue, it had been stated erroneously that the value must lie in the field of pn-th roots of unity; the correct condition is that the value must lie in the field of (pn-1)-th roots of unity. [Reported by Jack Schmidt]
  3. The function DirectProduct failed when one of the factors was known to be infinite.
  4. For a linear action homomorphism PreImageElm was very slow because there was no good method to check for injectivity, which is needed for nearly all good methods for PreImageElm. This change adds such a new method for IsInjective. [Reported by Akos Seress]
  5. Rare errors in the complement routine for permutation groups.
  6. Blocks code now uses jellyfish-style random elements to avoid bad Schreier trees.
  7. A method for IsPolycyclicGroup has been added. Such a method was missing so far.
  8. Corrected EpimorphismSchurCover to handle the trivial group correctly. Added new methods that follow immediately from computing the Schur Cover of a group. The attribute Epicentre, the operations NonabelianExteriorSquare and EpimorphismNonabelianExteriorSquare, and the property IsCentralFactor are added to the library with documentation and references.
  9. Display the correct expression in a call stack trace if an operation was called somewhere up due to the evaluation of a unary or binary operation.
  10. Made StripMemory an operation rather than a global function. Added ForgetMemory operation.
  11. Adjust things slightly to make later conversion to new vectors/matrices easier. Nothing of this should be visible.
  12. Corrected some details in the documentation of the GAP language. [Reported by Alexander Konovalov]
  13. Now PositionSorted is much faster on long mutable plain lists. (The former operation is substituted by a function and a new operation PositionSortedOp.) [Reported by Radu Silviu]
  14. Now it is possible to switch repeated warnings off when working with iterative polynomial rings.