Use of kron with more than two matricies

I have four 4x4 matricies called: ox, ru, cr, po.

I have been successful in using the Kronecker tensor product for two of the matricies, I being a 4x4 identity matrix.

mat = kron(I,ox) + kron(ru,I);

However, when I try doing the same with all four matricies...

mat = kron(I,I,I,ox) + kron(I,I,ru,I) + kron(I,cr,I,I) + kron(po,I,I,I);

I get an error saying 'Too many input arguments.'

Is here a way to achieve the result for four matricies?

Thank you.

Answer 1

[Matt J]

One way would be to use my KronProd class

https://www.mathworks.com/matlabcentral/fileexchange/25969-efficient-object-oriented-kronecker-product-manipulation

as follows,

kp=@(A,B,C,D) sparse(KronProd{D,C,B,A});

mat = kp(I,I,I,ox) + kp(I,I,ru,I) + kp(I,cr,I,I) + kp(po,I,I,I);

[Ashton Linney]

Thank you Matt! I have used the class and it has achieved what I was hoping for perfectly.

[Matt J]

You're welcome. You could also do it without the class, as follows,

kp=@(A,B,C,D) kron(kron(A,B),kron(C,D));

mat = kp(I,I,I,ox) + kp(I,I,ru,I) + kp(I,cr,I,I) + kp(po,I,I,I);