D'Alembert's and Wilson's functional equations for vector and $2\times 2$ matrix valued functions
Henrik Stetkær · MATHEMATICA SCANDINAVICA · 2000
We solve generalizations of d'Alembert's and Wilson's functional equations where the functions to be determined are defined on an abelian group G and take their values in C 2 or in the complex 2 Â 2 matrices.The solution formulas are expressed in the terms of the harmonic analysis on G : Complex characters, and additive and quadratic maps of G into CX MATH.