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Dear Gap-Forum,

I'm working on some small programs in gap, and I have the following 2 questions:

(I'm running a gap4r1 bugfix 1 version, compiled on a linux box

i686-pc-linux-gnu-gcc, with pargapmpi installed)

1. Consider the following strange behavior:

---BEGIN gap> G:=DihedralGroup(6); <pc group of size 6 with 2 generators> gap> tm:=TableOfMarks(G); TableOfMarks( Group( [ f1, f2 ] ) ) gap> H:=RepresentativeTom(tm,2); Group([ f2 ]) gap> th:=CharacterTable(H); CharacterTable( Group([ f2 ]) ) gap> Size(H); 2 gap> SizesConjugacyClasses(th); [ 1, 2/3, 2/3 ] gap> Display(tm); 1: 6 2: 3 1 3: 2 . 2 4: 1 1 1 1

gap> Display(th);

CT1

List Element: <list>[3] must have an assigned value at

cen[prime][i] := Number( fak, function ( x )

return x = prime;

end );

Display( tbl, rec(

) ); called from

<function>( <arguments> ) called from read-eval-loop

Entering break read-eval-print loop, you can 'quit;' to quit to outer loop,

or you can return after assigning a value to continue

brk>

---END

What am I doing wrong? What does it mean? How can I avoid this problem?

2. Is there a fast method to compute the isotropy subgroups of a representation

of an arbitrary group G (given the character)?

(i.e. the isotropy groups of the action of G on the space)

By counting the dimensions of the spaces fixed by its subgroups it is

possible to do it, but it's slow: do you know references to this problem?

Thank you very much in advance,

Davide Ferrario

Universita' di Milano-Bicocca

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