mirror of
https://github.com/vale981/arb
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110 lines
2.7 KiB
C
110 lines
2.7 KiB
C
/*=============================================================================
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This file is part of ARB.
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ARB 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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ARB 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 ARB; 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) 2016 Arb authors
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******************************************************************************/
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#include "bool_mat.h"
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/*
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* Cycle detection, following
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* https://en.wikipedia.org/wiki/Topological_sorting#Depth-first_search
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*/
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typedef struct
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{
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int *u; /* 'temporary mark' */
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int *v; /* 'permanent mark' */
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slong size;
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} _cycle_detection_s;
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static void
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_cycle_detection_init(_cycle_detection_s *s, slong size)
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{
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s->size = size;
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s->u = flint_calloc(size, sizeof(int));
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s->v = flint_calloc(size, sizeof(int));
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}
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static void
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_cycle_detection_clear(_cycle_detection_s *s)
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{
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flint_free(s->u);
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flint_free(s->v);
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}
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static int
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_cycle_detection_visit(_cycle_detection_s *s, const bool_mat_t A, slong n)
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{
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if (s->u[n])
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return 1;
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if (!s->v[n])
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{
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slong m;
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s->u[n] = 1;
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for (m = 0; m < s->size; m++)
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if (bool_mat_get_entry(A, n, m))
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if (_cycle_detection_visit(s, A, m))
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return 1;
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s->v[n] = 1;
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s->u[n] = 0;
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}
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return 0;
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}
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int
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bool_mat_is_nilpotent(const bool_mat_t A)
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{
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slong n;
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if (!bool_mat_is_square(A))
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{
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flint_printf("bool_mat_is_nilpotent: a square matrix is required!\n");
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abort();
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}
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if (bool_mat_is_empty(A))
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return 0;
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n = bool_mat_nrows(A);
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if (n == 1)
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{
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return !bool_mat_get_entry(A, 0, 0);
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}
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else
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{
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_cycle_detection_s s;
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slong i;
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int has_cycle;
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_cycle_detection_init(&s, n);
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for (has_cycle = 0, i = 0; !has_cycle && i < n; i++)
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if (!s.v[i])
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has_cycle = _cycle_detection_visit(&s, A, i);
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_cycle_detection_clear(&s);
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return !has_cycle;
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}
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}
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