pqc/external/flint-2.4.3/nmod_mat/solve_tril_recursive.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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) 2010,2011 Fredrik Johansson
******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_mat.h"
#include "nmod_vec.h"
void
nmod_mat_solve_tril_recursive(nmod_mat_t X,
const nmod_mat_t L, const nmod_mat_t B,
int unit)
{
nmod_mat_t LA, LC, LD, XX, XY, BX, BY;
slong r, n, m;
n = L->r;
m = B->c;
r = n / 2;
if (n == 0 || m == 0)
return;
/*
Denoting inv(M) by M^, we have:
[A 0]^ [X] == [A^ 0 ] [X] == [A^ X]
[C D] [Y] == [-D^ C A^ D^] [Y] == [D^ (Y - C A^ X)]
*/
nmod_mat_window_init(LA, L, 0, 0, r, r);
nmod_mat_window_init(LC, L, r, 0, n, r);
nmod_mat_window_init(LD, L, r, r, n, n);
nmod_mat_window_init(BX, B, 0, 0, r, m);
nmod_mat_window_init(BY, B, r, 0, n, m);
nmod_mat_window_init(XX, X, 0, 0, r, m);
nmod_mat_window_init(XY, X, r, 0, n, m);
nmod_mat_solve_tril(XX, LA, BX, unit);
nmod_mat_submul(XY, BY, LC, XX);
nmod_mat_solve_tril(XY, LD, XY, unit);
nmod_mat_window_clear(LA);
nmod_mat_window_clear(LC);
nmod_mat_window_clear(LD);
nmod_mat_window_clear(BX);
nmod_mat_window_clear(BY);
nmod_mat_window_clear(XX);
nmod_mat_window_clear(XY);
}