mapQtoR(Z)

function A  = mapQtoR(Z)
% A  = mapQtoR(Z)	Convert a quadrature matrix into its real equivalent.
% Each element in Z is represented by a 2x2 matrix in A: z -> [x -y; y x]
A = zeros(2*size(Z));
A(1:2:end,1:2:end) = real(Z);
A(2:2:end,2:2:end) = real(Z);
A(1:2:end,2:2:end) = -imag(Z);
A(2:2:end,1:2:end) = imag(Z);
return