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/*
Copyright (C) 2012,2018 Fredrik Johansson
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include "acb.h"
#include "acb_mat.h"
void
acb_mat_solve_lu_precomp(acb_mat_t X, const slong * perm,
const acb_mat_t A, const acb_mat_t B, slong prec)
{
slong i, j, c, n, m;
n = acb_mat_nrows(X);
m = acb_mat_ncols(X);
if (X == B)
{
acb_ptr tmp = flint_malloc(sizeof(acb_struct) * n);
for (c = 0; c < m; c++)
{
for (i = 0; i < n; i++)
tmp[i] = *acb_mat_entry(B, perm[i], c);
for (i = 0; i < n; i++)
*acb_mat_entry(X, i, c) = tmp[i];
}
flint_free(tmp);
}
else
{
for (c = 0; c < m; c++)
{
for (i = 0; i < n; i++)
{
acb_set(acb_mat_entry(X, i, c),
acb_mat_entry(B, perm[i], c));
}
}
}
/* solve_tril and solve_triu have some overhead */
if (n >= 4)
{
acb_mat_solve_tril(X, A, X, 1, prec);
acb_mat_solve_triu(X, A, X, 0, prec);
return;
}
for (c = 0; c < m; c++)
{
/* solve Ly = b */
for (i = 1; i < n; i++)
{
for (j = 0; j < i; j++)
{
acb_submul(acb_mat_entry(X, i, c),
acb_mat_entry(A, i, j), acb_mat_entry(X, j, c), prec);
}
}
/* solve Ux = y */
for (i = n - 1; i >= 0; i--)
{
for (j = i + 1; j < n; j++)
{
acb_submul(acb_mat_entry(X, i, c),
acb_mat_entry(A, i, j), acb_mat_entry(X, j, c), prec);
}
acb_div(acb_mat_entry(X, i, c), acb_mat_entry(X, i, c),
acb_mat_entry(A, i, i), prec);
}
}
}