Fast generalized Fourier transforms

M Clausen - Theoretical Computer Science, 1989 - Elsevier
M Clausen
Theoretical Computer Science, 1989Elsevier
Let G be af inite group. Then L s (G), the linear complexity of a suitable Wedderburn
transform corresponding to G, is smaller than 2·| G| 2. We improve this trivial upper bound by
showing that L s (G) is smaller than min {(s (T)− l (T))·| G|+ 7 q (T)·| G| 3 2, where the
minimum is taken over all towers T=(G n> G n− 1>⋯> G 0={1}) of subgroups of G= G n, and
where q (T)(resp. s (T)) is the maximum (resp. sum) of all indices [G i+ 1: G i] corresponding
to T and l (T)= n is the length of the tower. A similar upper bound is valid for the linear …
Let G be af inite group. Then L s (G), the linear complexity of a suitable Wedderburn transform corresponding to G, is smaller than 2·| G| 2. We improve this trivial upper bound by showing that L s (G) is smaller than min {(s (T)− l (T))·| G|+ 7 q (T)·| G| 3 2, where the minimum is taken over all towers T=(G n> G n− 1>⋯> G 0={1}) of subgroups of G= G n, and where q (T)(resp. s (T)) is the maximum (resp. sum) of all indices [G i+ 1: G i] corresponding to T and l (T)= n is the length of the tower. A similar upper bound is valid for the linear complexity of the inverse of such a Wedderburn transform. For symmetric groups our technique yields the stronger estimate L s (S n)= 0 (| S n|· log 3| S n|).
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