> < ^ Date: Fri, 10 May 2002 14:22:45 +0100 (BST)
> < ^ From: Leonard Soicher <l.h.soicher@qmul.ac.uk >
^ Subject: Announcing GRAPE 4.1 + program for fundamental groups and covers

Dear GAP-Forum,

I am pleased to announce a new release (version 4.1) of the GAP4
package GRAPE for computing with graphs and groups. GRAPE 4.1 is
included in the accepted packages archive of the newly released GAP 4.3
(available from http://www.gap-system.org ), or GRAPE 4.1 can be
downloaded on its own from http://www.gap-system.org/Share/grape.html
(where you can also browse the html manual and learn more about
GRAPE). Although GRAPE 4.1 should work with GAP 4.2, I strongly
recommend installing GAP 4.3.

I also wish to announce the availability of a GAP4/GRAPE4.x program for
computing fundamental groups, first homology groups, first homology
groups mod a prime, and covers of finite 2-dimensional simplicial
complexes. Visit http://www.maths.qmul.ac.uk/~leonard/fundamental/
for more information and to download the program.

The main changes to GRAPE from version 4.0 to 4.1 are listed below.
Please read these carefully as not all the changes are completely
backward compatible. There are some useful enhancements, and all known
bugs have been fixed.

Please email me ( L.H.Soicher@qmul.ac.uk ) if you install
GRAPE 4.1. I hope you enjoy using it.

Best regards, Leonard Soicher

Main changes from GRAPE 4.0 to GRAPE 4.1:
(1) Extended functionality of `CompleteSubgraphsOfGivenSize' so that a 
user can request only *maximal* complete subgraphs of a given size to
be returned.

(2) Extended functionality of `CompleteSubgraphs' and
`CompleteSubgraphsOfGivenSize' so that the required complete subgraphs
can be classified up to equivalence under the permutation group associated
with the input graph.

(3) Improvements to `CompleteSubgraphs' and `CompleteSubgraphsOfGivenSize'
which sometimes result in significant speed-ups.

(4) The default UNIX file permissions for GRAPE files now include write
permission for the owner. This is to make default file permissions more
in line with those of GAP.

(5) The naming convention for the vertices of the graphs output (in a
list) by `PartialLinearSpaces' has changed to be more consistent with
vertex-naming conventions in GRAPE. The point-vertices of such a graph
<delta> are 1,...,`<ptgraph>.order', with the name of point-vertex <i>
being the name of vertex <i> of <ptgraph>. A line-vertex of <delta>
is named by a list (not necessarily ordered) of the point-vertex names
for the points on that line.
Warning: This change is *not* backward compatible.

(6) For non-simple input graphs, different nauty parameters than
previously are set by `AutGroupGraph' and `SetAutGroupCanonicalLabelling'
(which is called by `IsIsomorphicGraph'). This is in order to avoid a
performance problem with certain sparse directed graphs.
Warning: canonical labellings may be different than before.

(7) Input graph to `CollapsedIndependentOrbitsGraph' must be simple.
(The function did not always produce correct output for non-simple graphs.)

(8) Bug fixed so that `AutGroupGraph' and `SetAutGroupCanonicalLabelling'
always output ranges as full lists for processing as input to

(9) Bug fixed in function `Girth'. This bug could cause wrong answers to
be returned.

(10) Improved documentation, including an example of research using GRAPE.

(11) Better file management for the non-GAP part of GRAPE.

(12) A p2c translation of tcfrontend4.p is now supplied and used.

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