RefElemData for hexes assumes tensor product quadrature and a tensor product structure. However, the M mass matrix is not necessarily a Kronecker product if the quadrature isn't tensor product, e.g., if we use a non-tensor product under-integrated quadrature.
RefElemDatafor hexes assumes tensor product quadrature and a tensor product structure. However, theMmass matrix is not necessarily a Kronecker product if the quadrature isn't tensor product, e.g., if we use a non-tensor product under-integrated quadrature.