On 25/09/2010, at 8:36 , Benjamin Sambale wrote: > Dear Forum, > > I've defined an action of a permutation group on a set of square matrices in > the following way: > > act:=function(x,g) > local i; > for i in [1..Length(x[1])] do x[i]:=Permuted(x[i],g); od; > return Permuted(x,g); > end; > > This works as expected, for example: > > gap> act([[1,2],[3,4]],(1,2)); > [ [ 4, 3 ], [ 2, 1 ] ] > > However, using the Orbit command gives > > gap> Orbit(Group((1,2)),[[1,2],[3,4]],act); > Lists Assignment: <list> must be a mutable list > > What is wrong here?
Your action tries to change the argument x (by assigning permuted rows). But this is probably not what you had intended anyway. Try the following. act:=function(x,g) local i, y; y := []; for i in [1..Length(x[1])] do y[i]:=Permuted(x[i],g); od; return Permuted(y,g); end; Cheers, Burkhard. _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
