Kronecker tensor product.
KRON(X,Y) is the Kronecker tensor product of X and Y.
The result is a large matrix formed by taking all possible
products between the elements of X and those of Y. For
example, if X is 2 by 3, then KRON(X,Y) is
[ X(1,1)*Y X(1,2)*Y X(1,3)*Y
X(2,1)*Y X(2,2)*Y X(2,3)*Y ]