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/*
Copyright (C) 2022 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 "gr_vec.h"
#include "gr_mat.h"
static void
_gr_mat_swap_rows(gr_mat_t mat, slong * perm, slong r, slong s, gr_ctx_t ctx)
{
if (r != s)
{
slong sz = ctx->sizeof_elem;
if (perm != NULL)
FLINT_SWAP(slong, perm[r], perm[s]);
_gr_vec_swap(GR_MAT_ENTRY(mat, r, 0, sz), GR_MAT_ENTRY(mat, s, 0, sz), mat->c, ctx);
}
}
int
gr_mat_lu_classical(slong * res_rank, slong * P, gr_mat_t LU, const gr_mat_t A, int rank_check, gr_ctx_t ctx)
{
gr_ptr d, e;
slong i, j, m, n, r, rank, row, col, sz;
int status = GR_SUCCESS;
int pivot_status;
m = gr_mat_nrows(A, ctx);
n = gr_mat_ncols(A, ctx);
rank = row = col = 0;
for (i = 0; i < m; i++)
P[i] = i;
if (m == 0 || n == 0)
{
*res_rank = 0;
return GR_SUCCESS;
}
sz = ctx->sizeof_elem;
status |= gr_mat_set(LU, A, ctx);
GR_TMP_INIT2(d, e, ctx);
#define ENTRY(ii, jj) GR_MAT_ENTRY(LU, ii, jj, sz)
while (row < m && col < n)
{
pivot_status = gr_mat_find_nonzero_pivot(&r, LU, row, m, col, ctx);
/* We don't know whether there is a nonzero pivot element,
so we can't determine the rank. */
if (pivot_status == GR_UNABLE)
{
status = GR_UNABLE;
break;
}
/* There is certainly no nonzero pivot element. */
if (pivot_status == GR_DOMAIN)
{
/* We proved that the matrix is rank-deficient,
accomplishing the goal. */
if (rank_check)
{
status = GR_SUCCESS;
rank = 0;
break;
}
/* Continue with next column. */
col++;
continue;
}
rank++;
if (r != row)
_gr_mat_swap_rows(LU, P, row, r, ctx);
/* Must be able to invert pivot element. */
status |= gr_inv(d, ENTRY(row, col), ctx);
if (status != GR_SUCCESS)
break;
for (j = row + 1; j < m; j++)
{
status |= gr_mul(e, ENTRY(j, col), d, ctx);
status |= gr_neg(e, e, ctx);
if (n - col - 1 > 0)
status |= _gr_vec_addmul_scalar(ENTRY(j, col + 1), ENTRY(row, col + 1), n - col - 1, e, ctx);
status |= gr_zero(ENTRY(j, col), ctx);
status |= gr_neg(ENTRY(j, rank - 1), e, ctx);
}
row++;
col++;
}
GR_TMP_CLEAR2(d, e, ctx);
#undef ENTRY
*res_rank = rank;
return status;
}