Forward Backward Substitution
// classes template < typename TT_DATA, unsigned int TP_DIM_SIZE, unsigned int TP_SUBST_TYPE, unsigned int TP_L_LEADING = 0, unsigned int TP_GRID_DIM = 1, unsigned int TP_NUM_FRAMES = 1, unsigned int TP_DIAG_INV = 0 > class xf::solver::aie::substitution::substitution_graph