The Substitution library element takes 2 operands, L and y. L is a lower-triangular matrix and y is a vector. L may be presented in either row-major or column-major
form because the IP supports the parameter TP_L_LEADING. The IP will perform any necessary transpose internally.
For backwards substitution, the Substitution library element still requires L, not the transpose conjugate of L. This convention allows the Substitution library element
to be used more easily in conjunction with the Cholesky library element to solve a set of linear equations because the Cholesky library element outputs L.