long nmod_poly_mat_nullspace(nmod_poly_mat_t res, const nmod_poly_mat_t mat) { long i, j, k, m, n, rank, nullity; long * pivots; long * nonpivots; nmod_poly_mat_t tmp; nmod_poly_t den; m = mat->r; n = mat->c; nmod_poly_init(den, nmod_poly_mat_modulus(mat)); nmod_poly_mat_init_set(tmp, mat); rank = nmod_poly_mat_rref(tmp, den, NULL, tmp); nullity = n - rank; nmod_poly_mat_zero(res); if (rank == 0) { for (i = 0; i < nullity; i++) nmod_poly_one(res->rows[i] + i); } else if (nullity) { pivots = flint_malloc(rank * sizeof(long)); nonpivots = flint_malloc(nullity * sizeof(long)); for (i = j = k = 0; i < rank; i++) { while (nmod_poly_is_zero(tmp->rows[i] + j)) { nonpivots[k] = j; k++; j++; } pivots[i] = j; j++; } while (k < nullity) { nonpivots[k] = j; k++; j++; } nmod_poly_set(den, tmp->rows[0] + pivots[0]); for (i = 0; i < nullity; i++) { for (j = 0; j < rank; j++) nmod_poly_set(res->rows[pivots[j]] + i, tmp->rows[j] + nonpivots[i]); nmod_poly_neg(res->rows[nonpivots[i]] + i, den); } flint_free(pivots); flint_free(nonpivots); } nmod_poly_clear(den); nmod_poly_mat_clear(tmp); return nullity; }
int nmod_poly_mat_inv(nmod_poly_mat_t Ainv, nmod_poly_t den, const nmod_poly_mat_t A) { slong n = nmod_poly_mat_nrows(A); if (n == 0) { nmod_poly_one(den); return 1; } else if (n == 1) { nmod_poly_set(den, E(A, 0, 0)); nmod_poly_one(E(Ainv, 0, 0)); return !nmod_poly_is_zero(den); } else if (n == 2) { nmod_poly_mat_det(den, A); if (nmod_poly_is_zero(den)) { return 0; } else if (Ainv == A) { nmod_poly_swap(E(A, 0, 0), E(A, 1, 1)); nmod_poly_neg(E(A, 0, 1), E(A, 0, 1)); nmod_poly_neg(E(A, 1, 0), E(A, 1, 0)); return 1; } else { nmod_poly_set(E(Ainv, 0, 0), E(A, 1, 1)); nmod_poly_set(E(Ainv, 1, 1), E(A, 0, 0)); nmod_poly_neg(E(Ainv, 0, 1), E(A, 0, 1)); nmod_poly_neg(E(Ainv, 1, 0), E(A, 1, 0)); return 1; } } else { nmod_poly_mat_t LU, I; slong * perm; int result; perm = _perm_init(n); nmod_poly_mat_init_set(LU, A); result = (nmod_poly_mat_fflu(LU, den, perm, LU, 1) == n); if (result) { nmod_poly_mat_init(I, n, n, nmod_poly_mat_modulus(A)); nmod_poly_mat_one(I); nmod_poly_mat_solve_fflu_precomp(Ainv, perm, LU, I); nmod_poly_mat_clear(I); } else nmod_poly_zero(den); if (_perm_parity(perm, n)) { nmod_poly_mat_neg(Ainv, Ainv); nmod_poly_neg(den, den); } _perm_clear(perm); nmod_poly_mat_clear(LU); return result; } }