function n = left_mtimes(k, x)%  Helper function for mtimes.m%%  if x is a scalar, use the property that%  x * kron(A, B) = kron(x * A, B)%%  if x is a vector such that x = vec(X),%  use the property that %  kron(A, B) * x = 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);elseif xsize(1) == kasize(2)*kbsize(2)   try      n = zeros(kasize(1) * kbsize(1), xsize(2));      for i = 1 : xsize(2)         tmp = reshape(x(:,i), kbsize(2), kasize(2));         tmp = k.b * tmp * k.a';         n(:,i) = reshape(tmp, kbsize(1) * kasize(1),1);      end   catch      error(lasterr)   endelseif ( kbsize(2) == xsize(1) & xsize(2) == kasize(2) )   n = k.b * x * k.a';end