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/*
Copyright (C) 2015 William Hart
Copyright (C) 2021 Daniel Schultz
Copyright (C) 2025 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.h"
#include "fmpz.h"
#include "fmpz_mod.h"
#include "fmpz_mod_mat.h"
int fmpz_mod_mat_reduce_row(slong * column, fmpz_mod_mat_t A, slong * P, slong * L,
slong m, const fmpz_mod_ctx_t ctx)
{
slong n = fmpz_mod_mat_ncols(A, ctx), i, j, r, res = -WORD(1);
fmpz_t d, h;
int status = GR_SUCCESS;
fmpz_init(d);
fmpz_init(h);
for (i = 0; i < n; i++)
{
if (i != 0)
fmpz_mod_set_fmpz(fmpz_mod_mat_entry(A, m, i),
fmpz_mod_mat_entry(A, m, i), ctx);
if (!fmpz_is_zero(fmpz_mod_mat_entry(A, m, i)))
{
r = P[i];
if (r != -WORD(1))
{
for (j = i + 1; j < L[r]; j++)
{
fmpz_submul(fmpz_mod_mat_entry(A, m, j),
fmpz_mod_mat_entry(A, r, j),
fmpz_mod_mat_entry(A, m, i));
}
fmpz_zero(fmpz_mod_mat_entry(A, m, i));
}
else
{
/* fmpz_mod_inv(h, fmpz_mod_mat_entry(A, m, i), ctx); */
fmpz_gcdinv(d, h, fmpz_mod_mat_entry(A, m, i), ctx->n);
if (!fmpz_is_one(d))
{
status = GR_DOMAIN;
goto cleanup;
}
fmpz_mod_set_ui(fmpz_mod_mat_entry(A, m, i), 1, ctx);
for (j = i + 1; j < L[m]; j++)
{
fmpz_mod_set_fmpz(fmpz_mod_mat_entry(A, m, j),
fmpz_mod_mat_entry(A, m, j), ctx);
fmpz_mod_mul(fmpz_mod_mat_entry(A, m, j),
fmpz_mod_mat_entry(A, m, j), h, ctx);
}
P[i] = m;
res = i;
break;
}
}
}
cleanup:
fmpz_clear(h);
fmpz_clear(d);
*column = res;
return status;
}