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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

nauty/dreadnaut.

(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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