Hi Lukas. If I understand your problem correctly, I believe the documentation link that you have provided contains your answer. In the section "B-form of Tensor Product Splines", the command given
Sp = spmat({s,t},a);
does what you are asking for. Here, the number vectors [m,n] are acquired from the size of "a", the coefficient matrix provided. With size of "s" and "t" known and the number vectors acquired, it also gets the orders vector [h,k].
So the equation is now in variable Sp.
