right_mtimes.m

curves ti si s a nice code.

function n = right_mtimes(x, k)
%  Helper function for mtimes.m
%
%  if x is a scalar, use the property that
%  kron(A, B) * x = kron(x * A, B)
%
%  if x is a vector such that x = vec(X)',
%  use the property that
%  x * kron(A, B) = vec(B' * X * A)'
%

kasize = size(k.a);
kbsize = size(k.b);
xsize = size(x);

if (length(x) == 1)
   n = kronMatrix(k.a * x, k.b);
else
   try
      n = zeros(xsize(1), kasize(2) * kbsize(2));
      for i = 1 : xsize(1)
         tmp = reshape(x(i,:), kbsize(1), kasize(1));
         tmp = k.b' * tmp * k.a;
         n(i,:) = reshape(tmp, 1, kbsize(2) * kasize(2));
      end
   catch
      error(lasterr)
   end
end