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/*
Copyright (C) 2023 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 "gr_mat.h"
truth_t gr_mat_is_diagonal(const gr_mat_t mat, gr_ctx_t ctx)
{
gr_method_vec_predicate is_zero = GR_VEC_PREDICATE(ctx, VEC_IS_ZERO);
slong ar, ac, i, sz = ctx->sizeof_elem;
truth_t eq, this_eq;
ar = gr_mat_nrows(mat, ctx);
ac = gr_mat_ncols(mat, ctx);
if (ar == 0 || ac == 0 || (ar == 1 && ac == 1))
return T_TRUE;
eq = T_TRUE;
for (i = 0; i < ar; i++)
{
/* upper triangular */
if (i >= 1)
{
this_eq = is_zero(GR_MAT_ENTRY(mat, i, 0, sz), FLINT_MIN(i, ac), ctx);
if (this_eq == T_FALSE)
return T_FALSE;
if (this_eq == T_UNKNOWN)
eq = T_UNKNOWN;
}
/* lower triangular */
if (i < ac - 1)
{
this_eq = is_zero(GR_MAT_ENTRY(mat, i, i + 1, sz), ac - i - 1, ctx);
if (this_eq == T_FALSE)
return T_FALSE;
if (this_eq == T_UNKNOWN)
eq = T_UNKNOWN;
}
}
return eq;
}