> < ^ From:

< ^ Subject:

David Sibley writes in his e-mail message of 1993/03/15

This is with 3.2 running on a Sun Sparcstation 1+ with the distributed

binary obtained from wuarchive.wustl.edu. Looks like it is asking for

the length of a non-existant list. Other than that, I have no idea

what the trouble is.

I'd appreciate a workaround.

gap> g:=ThreeGroup(243,4);;

gap> h:=ThreeGroup(243,5);;

gap> gt:=CharTablePGroup(g);;

gap> ht:=CharTablePGroup(h);;

gap> x:=TransformingPermutationsCharTables(gt,ht);

Error, List Element: <list>[6] must have a value at

return Length( fam1.permutations[x] )

<> Length( fam1.permutations[bij_rows[x]] ) ... in

func( l ) called from

ForAny( [ 1 .. Length( bij_rows ) ], function ( x ) ... end ) called from

TransformingPermutations( tbl1.irreducibles, tbl2.irreducibles ) called from

TransformingPermutationsCharTables( gt, ht ) called from

This function was written by Tomas Breuer and I don't pretend to fully

understand it, so take my comments with a grain of salt.

It seems that this problem can only happen if there is no transforming

permutation. I hope this is enough of a workaround.

More background. 'TransformingPermutations' first groups the characters

of each table in families. Two characters are in a family if they are

equal when sorted (e.g., '[1,-1,1,-1]' is in the same family as

'[1,1,-1,-1]', but not in the same family as '[1,-1,-1,-1]'). A

necessary condition for the existence of a transforming permutation is a

bijection between the list of families, i.e., every family of 'gt' must

also be a family of 'ht' (this is tested twice), and every family of 'ht'

must also be a family of 'gt' (this is *not* tested). The test that

fails is the test that the corresponding families of 'gt' and 'ht' also

have the same number of characters in them.

David writes in another e-mail message of 1993/03/15

It looks like the problem may actually be with ForAny. From what I can

see in the documentation, the following should work (returning false)

but does not. It's not clear that this is the same bug. The error

message is different.gap> a:=[1,2]; [ 1, 2 ] gap> ForAny([a,a,,,a,a],x->Length[x]>2); Error, List Element: <position> must be a positive integer at

And in yet another e-mail message

Arrgh. Ignore that about ForAny. Soon I hope to learn the difference

between parentheses and square brackets.

Have you been using Mathematica lately? ;-)

Martin.

-- .- .-. - .. -. .-.. --- ...- . ... .- -. -. .. -.- .- Martin Sch"onert, Martin.Schoenert@Math.RWTH-Aachen.DE, +49 241 804551 Lehrstuhl D f"ur Mathematik, Templergraben 64, RWTH, D 51 Aachen, Germany

> < [top]