74 lines
2.3 KiB
C
74 lines
2.3 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) 2010,2011 Fredrik Johansson
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******************************************************************************/
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#include <stdlib.h>
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#include <gmp.h>
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#include "flint.h"
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#include "nmod_mat.h"
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#include "nmod_vec.h"
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void
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nmod_mat_solve_triu_recursive(nmod_mat_t X,
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const nmod_mat_t U, const nmod_mat_t B,
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int unit)
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{
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nmod_mat_t UA, UB, UD, XX, XY, BX, BY;
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slong r, n, m;
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n = U->r;
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m = B->c;
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r = n / 2;
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if (n == 0 || m == 0)
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return;
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/*
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Denoting inv(M) by M^, we have:
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[A B]^ [X] == [A^ (X - B D^ Y)]
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[0 D] [Y] == [ D^ Y ]
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*/
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nmod_mat_window_init(UA, U, 0, 0, r, r);
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nmod_mat_window_init(UB, U, 0, r, r, n);
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nmod_mat_window_init(UD, U, r, r, n, n);
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nmod_mat_window_init(BX, B, 0, 0, r, m);
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nmod_mat_window_init(BY, B, r, 0, n, m);
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nmod_mat_window_init(XX, X, 0, 0, r, m);
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nmod_mat_window_init(XY, X, r, 0, n, m);
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nmod_mat_solve_triu(XY, UD, BY, unit);
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nmod_mat_submul(XX, BX, UB, XY);
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nmod_mat_solve_triu(XX, UA, XX, unit);
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nmod_mat_window_clear(UA);
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nmod_mat_window_clear(UB);
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nmod_mat_window_clear(UD);
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nmod_mat_window_clear(BX);
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nmod_mat_window_clear(BY);
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nmod_mat_window_clear(XX);
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nmod_mat_window_clear(XY);
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}
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