102 lines
2.7 KiB
C
102 lines
2.7 KiB
C
/*=============================================================================
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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 "fmpz_mat.h"
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#include "fmpz.h"
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void
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fmpz_mat_randdet(fmpz_mat_t mat, flint_rand_t state, const fmpz_t det)
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{
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slong i, j, k, n;
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int parity;
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fmpz * diag;
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fmpz_factor_t factor;
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n = mat->r;
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if (n != mat->c)
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{
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flint_printf("Exception (fmpz_mat_randdet). Non-square matrix.\n");
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abort();
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}
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if (n < 1)
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return;
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/* Start with the zero matrix */
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fmpz_mat_zero(mat);
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if (*det == WORD(0))
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return;
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fmpz_factor_init(factor);
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fmpz_factor(factor, det);
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diag = _fmpz_vec_init(n);
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for (i = 0; i < n; i++)
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fmpz_one(&diag[i]);
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/* Form diagonal entries that multiply to the determinant */
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for (i = 0; i < factor->num; i++)
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{
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for (j = 0; j < factor->exp[i]; j++)
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{
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k = n_randint(state, n);
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fmpz_mul(&diag[k], &diag[k], &factor->p[i]);
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}
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}
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/* Reverse signs an even number of times */
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for (i = 0; i < 2*n; i++)
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{
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k = n_randint(state, n);
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fmpz_neg(&diag[k], &diag[k]);
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}
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if (factor->sign == -1)
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fmpz_neg(&diag[0], &diag[0]);
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parity = fmpz_mat_randpermdiag(mat, state, diag, n);
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/* Need another reversal if the permutation was odd */
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if (parity)
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{
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for (i = 0; i < mat->r; i++)
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{
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for (j = 0; j < mat->c; j++)
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{
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if (!fmpz_is_zero(mat->rows[i] + j))
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{
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fmpz_neg(mat->rows[i] + j, mat->rows[i] + j);
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goto end;
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}
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}
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}
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}
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end:
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_fmpz_vec_clear(diag, n);
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fmpz_factor_clear(factor);
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}
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