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/*=============================================================================
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 Fredrik Johansson
******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include "flint.h"
#include "ulong_extras.h"
#include "nmod_vec.h"
#include "nmod_mat.h"
static __inline__ int
nmod_mat_pivot(nmod_mat_t A, slong * P, slong start_row, slong col)
{
slong j, t;
mp_ptr u;
if (nmod_mat_entry(A, start_row, col) != 0)
return 1;
for (j = start_row + 1; j < A->r; j++)
{
if (nmod_mat_entry(A, j, col) != 0)
{
u = A->rows[j];
A->rows[j] = A->rows[start_row];
A->rows[start_row] = u;
t = P[j];
P[j] = P[start_row];
P[start_row] = t;
return -1;
}
}
return 0;
}
slong
nmod_mat_lu_classical(slong * P, nmod_mat_t A, int rank_check)
{
mp_limb_t d, e, **a;
nmod_t mod;
slong i, m, n, rank, length, row, col;
m = A->r;
n = A->c;
a = A->rows;
mod = A->mod;
rank = row = col = 0;
for (i = 0; i < m; i++)
P[i] = i;
while (row < m && col < n)
{
if (nmod_mat_pivot(A, P, row, col) == 0)
{
if (rank_check)
return 0;
col++;
continue;
}
rank++;
d = a[row][col];
d = n_invmod(d, mod.n);
length = n - col - 1;
for (i = row + 1; i < m; i++)
{
e = n_mulmod2_preinv(a[i][col], d, mod.n, mod.ninv);
if (length != 0)
_nmod_vec_scalar_addmul_nmod(a[i] + col + 1,
a[row] + col + 1, length, nmod_neg(e, mod), mod);
a[i][col] = 0;
a[i][rank - 1] = e;
}
row++;
col++;
}
return rank;
}
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