105 lines
2.9 KiB
C
105 lines
2.9 KiB
C
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/*=============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2010 Fredrik Johansson
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******************************************************************************/
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#include "flint.h"
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#include "nmod_poly.h"
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#include "nmod_poly_mat.h"
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#include "perm.h"
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#define E nmod_poly_mat_entry
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int
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nmod_poly_mat_inv(nmod_poly_mat_t Ainv, nmod_poly_t den,
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const nmod_poly_mat_t A)
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{
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slong n = nmod_poly_mat_nrows(A);
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if (n == 0)
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{
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nmod_poly_one(den);
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return 1;
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}
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else if (n == 1)
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{
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nmod_poly_set(den, E(A, 0, 0));
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nmod_poly_one(E(Ainv, 0, 0));
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return !nmod_poly_is_zero(den);
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}
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else if (n == 2)
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{
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nmod_poly_mat_det(den, A);
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if (nmod_poly_is_zero(den))
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{
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return 0;
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}
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else if (Ainv == A)
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{
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nmod_poly_swap(E(A, 0, 0), E(A, 1, 1));
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nmod_poly_neg(E(A, 0, 1), E(A, 0, 1));
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nmod_poly_neg(E(A, 1, 0), E(A, 1, 0));
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return 1;
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}
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else
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{
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nmod_poly_set(E(Ainv, 0, 0), E(A, 1, 1));
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nmod_poly_set(E(Ainv, 1, 1), E(A, 0, 0));
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nmod_poly_neg(E(Ainv, 0, 1), E(A, 0, 1));
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nmod_poly_neg(E(Ainv, 1, 0), E(A, 1, 0));
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return 1;
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}
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}
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else
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{
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nmod_poly_mat_t LU, I;
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slong * perm;
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int result;
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perm = _perm_init(n);
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nmod_poly_mat_init_set(LU, A);
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result = (nmod_poly_mat_fflu(LU, den, perm, LU, 1) == n);
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if (result)
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{
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nmod_poly_mat_init(I, n, n, nmod_poly_mat_modulus(A));
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nmod_poly_mat_one(I);
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nmod_poly_mat_solve_fflu_precomp(Ainv, perm, LU, I);
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nmod_poly_mat_clear(I);
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}
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else
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nmod_poly_zero(den);
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if (_perm_parity(perm, n))
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{
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nmod_poly_mat_neg(Ainv, Ainv);
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nmod_poly_neg(den, den);
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}
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_perm_clear(perm);
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nmod_poly_mat_clear(LU);
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return result;
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}
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}
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