pqc/external/flint-2.4.3/nmod_poly_mat/rref.c
2014-05-24 23:16:06 +02:00

112 lines
3.4 KiB
C

/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011-2012 Fredrik Johansson
******************************************************************************/
#include "flint.h"
#include "nmod_poly.h"
#include "nmod_poly_mat.h"
slong
nmod_poly_mat_rref(nmod_poly_mat_t R, nmod_poly_t den, const nmod_poly_mat_t A)
{
slong i, j, k, m, n, rank;
slong *pivots, *nonpivots;
rank = nmod_poly_mat_fflu(R, den, NULL, A, 0);
m = nmod_poly_mat_nrows(R);
n = nmod_poly_mat_ncols(R);
/* clear bottom */
for (i = rank; i < m; i++)
for (j = 0; j < n; j++)
nmod_poly_zero(nmod_poly_mat_entry(R, i, j));
/* Convert row echelon form to reduced row echelon form */
if (rank > 1)
{
nmod_poly_t tmp, tmp2;
nmod_poly_init(tmp, nmod_poly_mat_modulus(R));
nmod_poly_init(tmp2, nmod_poly_mat_modulus(R));
pivots = flint_malloc(sizeof(slong) * n);
nonpivots = pivots + rank;
/* find pivot positions */
for (i = j = k = 0; i < rank; i++)
{
while (nmod_poly_is_zero(nmod_poly_mat_entry(R, i, j)))
{
nonpivots[k] = j;
k++;
j++;
}
pivots[i] = j;
j++;
}
while (k < n - rank)
{
nonpivots[k] = j;
k++;
j++;
}
for (k = 0; k < n - rank; k++)
{
for (i = rank - 2; i >= 0; i--)
{
nmod_poly_mul(tmp, den, nmod_poly_mat_entry(R, i, nonpivots[k]));
for (j = i + 1; j < rank; j++)
{
nmod_poly_mul(tmp2, nmod_poly_mat_entry(R, i, pivots[j]),
nmod_poly_mat_entry(R, j, nonpivots[k]));
nmod_poly_sub(tmp, tmp, tmp2);
}
nmod_poly_div(nmod_poly_mat_entry(R, i, nonpivots[k]),
tmp, nmod_poly_mat_entry(R, i, pivots[i]));
}
}
/* clear pivot columns */
for (i = 0; i < rank; i++)
{
for (j = 0; j < rank; j++)
{
if (i == j)
nmod_poly_set(nmod_poly_mat_entry(R, j, pivots[i]), den);
else
nmod_poly_zero(nmod_poly_mat_entry(R, j, pivots[i]));
}
}
flint_free(pivots);
nmod_poly_clear(tmp);
nmod_poly_clear(tmp2);
}
return rank;
}