On Mon, Apr 06, 2015 at 08:44:39PM +0100, Jim Talbert wrote: > Hi all, > > I have ay simple question. I am utilizing GAP in a way that necessitates > the construction of explicit matrix representations of group generators. > These matrices can in my case depend on things like x^(1/4), e.g. > ER(ER(x)). However, the ER command can only deal with rational arguments, > so ER(ER(16))=2 works fine, but ER(ER(8)) is problematic. I have looked > through the documentation and don't see an obvious way to get around the > problem. Can anyone help?
ER(ER(8)) is not a cyclotomic number, so it cannot be represented this way. What you can do is to use the monomorphism: GL_n(K(ER(x))) -> GL_(2*n)(K). which replace the coefficient a+b*ER(x) by the matrix [[a,b*x],[b,a]] You will get larger matrices with simpler coefficients. Cheers, Bill. _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
