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GAP 4.4 Update 7 (March 2006)

New or improved functionality

  1. The Display functionality for character tables has been extended by addition of an option to show power maps and centralizer orders in a format similar to that used in the ATLAS. Furthermore the options handling is now hierarchical, in order to admit more flexible overloading.
  2. For the function LowIndexSubgroupsFpGroup, there is now an iterator variant LowIndexSubgroupsFpGroupIterator. [Suggested (and based on code contributed) by Michael Hartley]
  3. Semigroup functionality in GAP has been improved and extended. Green's relations are now stored differently, making the system more amenable to new methods for computing these relations in special cases. It is now possible to calculate Green's classes etc. without computing the entire semigroup or necessarily loading the package MONOID. Furthermore, the Froidure-Pin algorithm has now been implemented in GAP.
  4. Functionality for creating free products of any list of groups for which a finite presentation can be determined had been added. This function returns a finitely presented group. This functionality includes the Embedding operation. As an application of this new code a specialized direct product operation has been added for finitely presented groups which returns a finitely presented group. This application includes Embedding and Projection functionality.
  5. Some new Straight Line Program (SLP) functionality has been added. The new functions take given SLPs and create new ones by restricting to a subset of the results, or to an intermediate result or by calculating the product of the results of two SLPs.
  6. New code has been added to allow group elements with memory; that is, they store automatically how they were derived from some given set of generators. Note that there is not yet documentation for this functionality, but some packages already use it.
  7. New code has been added to handle matrices and vectors in such a way that they do not change their representation in a generic manner.
  8. The Irr method for p-solvable p-modular Brauer tables now keeps the order of the irreducibles in the ordinary table.
  9. GAP can now handle any finite field for which the Conway polynomial is known or can be computed.
  10. New Conway polynomials provided by John Bray and Kate Minola have been added.
  11. The ReadTest methods for strings (filenames) and streams now automatically set the screen width (see SizeScreen) to 80 before the tests, and reset it afterwards.
  12. Now a few more checks are done during the configure phase of compiling for future use of some I/O functions of the C-library in a package. Also the path to the GAP binaries for the GAP compiler is now handled via autoconf. Finally, now autoconf version 2.59 is used.

Fixed bugs which could produce wrong results

  1. Some technical errors in the functions for compressed vectors and matrices which could lead to corruption of internal data structures and so to crashes or conceivably to wrong results. [Reported by Roman Schmied]
  2. A potential problem in the generic method for the undocumented operation DirectFactorsOfGroup: It was silently assumed that NormalSubgroups delivers the trivial subgroup as first and the whole group as last entry of the resulting list.
  3. The code for sublists of compressed vectors created by vec{range} may write one byte beyond the space allocated for the new vector, overwriting part of the next object in the workspace. Thanks to Jack Schmidt for narrowing down the problem.
  4. Given a class function object of value zero, an InverseOp method for a class function erroneously did not return fail. [Reported by Jack Schmidt]
  5. The Order method for a class function erroneously returned a finite number if one of the values was nonreal, not a cyclotomic integer, and had norm 1.
  6. Two missing perfect groups were added, and the permutation degree lowered on the perfect groups with the largest degrees. [Reported by Jack Schmidt]
  7. When a character table was displayed with Display, the centralizer order displayed for the first class shown was not correct if it did not involve all prime divisors of the group. [Reported by Jack Schmidt]
  8. The first argument of the function VectorSpace must be a field. This is checked from now on. [Reported by Laurent Bartholdi]
  9. Up to now, it was possible to create a group object from a semigroup of cyclotomics using AsGroup, although groups of cyclotomics are not admissible. [Reported by Alexander Konovalov]
  10. The documentation of CharacteristicPolynomial(F,mat) was ambiguous if FieldOfMatrix(mat) ≤ F < DefaultFieldOfMatrix(mat). In particular, the result was representation dependent. This was fixed by introducing a second field which specifies the vector space which mat acts upon. [Reported by Jack Schmidt]
  11. AssociatedReesMatrixSemigroupOfDClass produced an incorrect sandwich matrix for the semigroup created. This matrix is an attribute set when creating the Rees matrix semigroup but is not used for creating the semigroup. The incorrect result was returned when SandwichMatrix was called. [Reported by Nelson Silva and Joao Araujo]
  12. The literal "compiled" was given an incorrect length. The kernel was then unable to find compiled library code as the search path was incorrect. Also the documentation example had an error in the path used to invoke the gac compiler.
  13. The twisting group in a generic wreath product might have had intransitive action. [Reported by Laurent Bartholdi]
  14. There was an arithmetic bug in the polynomial reduction code.

Fixed bugs which could lead to crashes

  • Bug 1 in the list of fixed bugs which could lead to wrong results could also potentially lead to crashes.

Other fixed bugs

  1. The matrices of invariant forms stored as values of the attributes InvariantBilinearForm, InvariantQuadraticForm, and InvariantSesquilinearForm, for matrix groups over finite fields, are now in the (compressed) format returned by ImmutableMatrix.
  2. String now returns an immutable string, by making a copy before changing the argument.
  3. Permutation ^0 and permutation ^1 were not handled with special code in the kernel, hence were very slow for big permutations. [Reported by Max Neunhoeffer]
  4. Added code to cache the induced pcgs for an arbitrary parent pcgs. (This code was formerly part of the CRISP package.)
  5. This fix consists of numerous changes to improve support for direct products, including: - new methods for PcgsElementaryAbelianSeries, PcgsChiefSeries, ExponentsOfPcElement, DepthOfPcElement for direct products - fixed EnumeratorOfPcgs to test for membership first - new methods for membership test in groups which have an induced pcgs - added GroupOfPcgs attribute to pcgs in various methods - fixed declarations of PcgsElementaryAbelianSeries, PcgsChiefSeries (the declared argument was a pcgs, not a group) [Reported by Roman Schmied]
  6. Corrected a term ordering problem encountered by the basis construction code for finite dimensional vector spaces of multivariate rational functions. [Reported by Jan Draisma]
  7. When the factor of a finite dimensional group ring by an ideal was formed, a method intended for free algebras modulo relations was used, and the returned factor algebra could be used for (almost) nothing. [Reported by Heiko Dietrich]
  8. Up to now, PowerMap ran into an error when one asked for the n-th power map where n was not a small integer. This happened in some GAP library functions if the exponent of the character table in question was not a small integer.
  9. Up to now, the test whether a finite field element was contained in a group of finite field elements ran into an error if the element was not in the field generated by the group elements. [Reported by Heiko Dietrich]
  10. Conjugacy classes of natural (special) linear groups are now always returned with trivial class first.
  11. Up to now, it could happen that CheckFixedPoints reduced an entry in its second argument to a list containing only one integer but did not replace the list by that integer; according to the conventions, this replacement should be done.
  12. The functions PrintTo and AppendTo did not work correctly for streams. [Reported by Marco Costantini]
  13. The function Basis did not return a value when it was called with the argument Rationals. [Reported by Klaus Lux]
  14. For certain matrix groups, the function StructureDescription raised an error message. The reason for this was that a trivial method for IsGeneralLinearGroup for matrix groups in lib/grpmat.gi which is ranked higher than the nontrivial method for generic groups in lib/grpnames.gi called the operation IsNaturalGL, for which there was no nontrivial method available. [Reported by Nilo de Roock]
  15. Action on sets of length 1 was not correctly handled. [Reported by Mathieu Dutour]
  16. Now WriteByte admits writing zero characters to all streams. [Reported by Marco Costantini]
  17. The conjugacy test for subgroups tests for elementary abelian regular normal subgroup (EARNS) conjugacy. The fix will catch this in the case that the second group has no EARNS. [Reported by Andrew Johnson]
  18. So far, the UNIX installation didn't result in a correct gap.sh if the installation path contained space characters. Now it should handle this case correctly, as well as other unusual characters in path names (except for double quotes).
The GAP Group Last updated: Fri Mar 17 11:16:41 2006