 A ...... if Na&gt;0, cell array of A{k} for k=1,...,Na each defining
          one matrix constraint; let's assume that A{k} has maximal
          order maxOrder and has nMat matrices defined, then A{k} should
          have the following elements:
            A{k}.Q - cell array of nMat (sparse) matrices of the same
               dimension
            A{k}.midx - (maxOrder x nMat) matrix defining the multi-indices
               for each matrix Q; use 0 within the multi-index to reduce
               the