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Dear Gap-forum, and Nicola,

I would express the algebraic numbers occuring in your example in a suitable cyclotomic field (see E and CF in the manual); in your case CF(20) should do; for instance, cos(t) and sin(t) should be sg like this: c1:=(-E(5)^2-E(5)^3)/2; s1:=(-E(5)^2+E(5)^3)/(2*E(4)); Then define A and S, and simply call Size(Group([A,S])).

Best wishes,

Jan

Dear GAP forum,

I'd like to generate a group using two elements A and S: G = <A,S>. I

don't know if this group is finite. Someone can help me?S = diag(1,1,-1,-1) A = [0, 0, cos(s), -sin(s)] [-sin(t), cos(t), 0, 0] [cos(t), sin(t), 0, 0] [0, 0, sin(s), cos(s)]with

cos(t) := 1/4 + 1/4 sqrt(5) sin(t) := 1/4 sqrt(2) sqrt(5 - sqrt(5)) cos(s):= 3/4 - 1/4 sqrt(5) sin(s):= 1/4 sqrt(2 + 6 sqrt(5))Thank you, Nicola.

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