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/*!
\file vector/neta/components.c
\brief Network Analysis library - graph components
Computes strongly and weakly connected components.
(C) 2009-2010 by Daniel Bundala, and the GRASS Development Team
This program is free software under the GNU General Public License
(>=v2). Read the file COPYING that comes with GRASS for details.
\author Daniel Bundala (Google Summer of Code 2009)
\author Markus Metz
*/
/* example:
*
* X -->-- X ---- X --<-- X ---- X
* N1 N2 N3 N4 N5
*
* -->--, --<-- one-way
* ---- both ways
*
* weakly connected:
* all 5 nodes, even though there is no direct path from N1 to N4, 5
* but N1 connects to N2, 3, and N4, 5 also connect to N2, 3
*
* strongly connected:
* no path from N2 to N1, no path from N3 to N4
* component 1: N1
* component 2: N2, 3
* Component3: N4, 5
*/
#include <stdio.h>
#include <stdlib.h>
#include <grass/gis.h>
#include <grass/vector.h>
#include <grass/glocale.h>
#include <grass/dgl/graph.h>
/*!
\brief Computes weakly connected components
\param graph input graph
\param[out] component array of component ids
\return number of components
\return -1 on failure
*/
int NetA_weakly_connected_components(dglGraph_s *graph, int *component)
{
int nnodes, i;
dglInt32_t *stack;
int stack_size, components;
dglInt32_t *cur_node;
dglNodeTraverser_s nt;
int have_node_costs;
dglInt32_t ncost;
if (graph->Version < 2) {
G_warning("Directed graph must be version 2 or 3 for "
"NetA_weakly_connected_components()");
return -1;
}
components = 0;
nnodes = dglGet_NodeCount(graph);
stack = (dglInt32_t *)G_calloc(nnodes + 1, sizeof(dglInt32_t));
if (!stack) {
G_fatal_error(_("Out of memory"));
return -1;
}
for (i = 1; i <= nnodes; i++)
component[i] = 0;
ncost = 0;
have_node_costs = dglGet_NodeAttrSize(graph);
dglNode_T_Initialize(&nt, graph);
for (cur_node = dglNode_T_First(&nt); cur_node;
cur_node = dglNode_T_Next(&nt)) {
dglInt32_t cur_node_id = dglNodeGet_Id(graph, cur_node);
if (!component[cur_node_id]) {
stack[0] = cur_node_id;
stack_size = 1;
component[cur_node_id] = ++components;
while (stack_size) {
dglInt32_t *node, *edgeset, *edge;
dglEdgesetTraverser_s et;
node = dglGetNode(graph, stack[--stack_size]);
edgeset = dglNodeGet_OutEdgeset(graph, node);
dglEdgeset_T_Initialize(&et, graph, edgeset);
for (edge = dglEdgeset_T_First(&et); edge;
edge = dglEdgeset_T_Next(&et)) {
dglInt32_t to;
to = dglNodeGet_Id(graph, dglEdgeGet_Tail(graph, edge));
if (!component[to]) {
component[to] = components;
/* do not go through closed nodes */
if (have_node_costs) {
memcpy(&ncost,
dglNodeGet_Attr(
graph, dglEdgeGet_Tail(graph, edge)),
sizeof(ncost));
}
if (ncost >= 0)
stack[stack_size++] = to;
}
}
dglEdgeset_T_Release(&et);
edgeset = dglNodeGet_InEdgeset(graph, node);
dglEdgeset_T_Initialize(&et, graph, edgeset);
for (edge = dglEdgeset_T_First(&et); edge;
edge = dglEdgeset_T_Next(&et)) {
dglInt32_t to;
to = dglNodeGet_Id(graph, dglEdgeGet_Head(graph, edge));
if (!component[to]) {
component[to] = components;
/* do not go through closed nodes */
if (have_node_costs) {
memcpy(&ncost,
dglNodeGet_Attr(
graph, dglEdgeGet_Tail(graph, edge)),
sizeof(ncost));
}
if (ncost >= 0)
stack[stack_size++] = to;
}
}
dglEdgeset_T_Release(&et);
}
}
}
dglNode_T_Release(&nt);
G_free(stack);
return components;
}
/*!
\brief Computes strongly connected components with Kosaraju's
two-pass algorithm
\param graph input graph
\param[out] component array of component ids
\return number of components
\return -1 on failure
*/
int NetA_strongly_connected_components(dglGraph_s *graph, int *component)
{
int nnodes, i;
dglInt32_t *stack, *order;
int *processed;
int stack_size, order_size, components;
dglInt32_t *cur_node;
dglNodeTraverser_s nt;
int have_node_costs;
dglInt32_t ncost;
if (graph->Version < 2) {
G_warning("Directed graph must be version 2 or 3 for "
"NetA_strongly_connected_components()");
return -1;
}
components = 0;
nnodes = dglGet_NodeCount(graph);
stack = (dglInt32_t *)G_calloc(nnodes + 1, sizeof(dglInt32_t));
order = (dglInt32_t *)G_calloc(nnodes + 1, sizeof(dglInt32_t));
processed = (int *)G_calloc(nnodes + 1, sizeof(int));
if (!stack || !order || !processed) {
G_fatal_error(_("Out of memory"));
return -1;
}
for (i = 1; i <= nnodes; i++) {
component[i] = 0;
}
ncost = 0;
have_node_costs = dglGet_NodeAttrSize(graph);
order_size = 0;
dglNode_T_Initialize(&nt, graph);
for (cur_node = dglNode_T_First(&nt); cur_node;
cur_node = dglNode_T_Next(&nt)) {
dglInt32_t cur_node_id = dglNodeGet_Id(graph, cur_node);
if (!component[cur_node_id]) {
component[cur_node_id] = --components;
stack[0] = cur_node_id;
stack_size = 1;
while (stack_size) {
dglInt32_t *node, *edgeset, *edge;
dglEdgesetTraverser_s et;
dglInt32_t node_id = stack[stack_size - 1];
if (processed[node_id]) {
stack_size--;
order[order_size++] = node_id;
continue;
}
processed[node_id] = 1;
node = dglGetNode(graph, node_id);
edgeset = dglNodeGet_OutEdgeset(graph, node);
dglEdgeset_T_Initialize(&et, graph, edgeset);
for (edge = dglEdgeset_T_First(&et); edge;
edge = dglEdgeset_T_Next(&et)) {
dglInt32_t to;
to = dglNodeGet_Id(graph, dglEdgeGet_Tail(graph, edge));
if (!component[to]) {
component[to] = components;
/* do not go through closed nodes */
if (have_node_costs) {
memcpy(&ncost,
dglNodeGet_Attr(
graph, dglEdgeGet_Tail(graph, edge)),
sizeof(ncost));
}
if (ncost < 0)
processed[to] = 1;
stack[stack_size++] = to;
}
}
dglEdgeset_T_Release(&et);
}
}
}
dglNode_T_Release(&nt);
components = 0;
dglNode_T_Initialize(&nt, graph);
while (order_size) {
dglInt32_t cur_node_id = order[--order_size];
int cur_comp = component[cur_node_id];
if (cur_comp < 1) {
component[cur_node_id] = ++components;
stack[0] = cur_node_id;
stack_size = 1;
while (stack_size) {
dglInt32_t *node, *edgeset, *edge;
dglEdgesetTraverser_s et;
dglInt32_t node_id = stack[--stack_size];
node = dglGetNode(graph, node_id);
edgeset = dglNodeGet_InEdgeset(graph, node);
dglEdgeset_T_Initialize(&et, graph, edgeset);
for (edge = dglEdgeset_T_First(&et); edge;
edge = dglEdgeset_T_Next(&et)) {
dglInt32_t to;
to = dglNodeGet_Id(graph, dglEdgeGet_Head(graph, edge));
if (component[to] == cur_comp) {
component[to] = components;
/* do not go through closed nodes */
if (have_node_costs) {
memcpy(&ncost,
dglNodeGet_Attr(
graph, dglEdgeGet_Head(graph, edge)),
sizeof(ncost));
}
if (ncost >= 0)
stack[stack_size++] = to;
}
}
dglEdgeset_T_Release(&et);
}
}
}
dglNode_T_Release(&nt);
G_free(stack);
G_free(order);
G_free(processed);
return components;
}
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