int igraph_difference(igraph_t *res,
const igraph_t *orig, const igraph_t *sub) {
/* Quite nasty, but we will use that an edge adjacency list
contains the vertices according to the order of the
vertex ids at the "other" end of the edge. */
long int no_of_nodes_orig=igraph_vcount(orig);
long int no_of_nodes_sub =igraph_vcount(sub);
long int no_of_nodes=no_of_nodes_orig;
long int smaller_nodes;
igraph_bool_t directed=igraph_is_directed(orig);
igraph_vector_t edges;
igraph_vector_t edge_ids;
igraph_vector_t *nei1, *nei2;
igraph_inclist_t inc_orig, inc_sub;
long int i;
igraph_integer_t v1, v2;
if (directed != igraph_is_directed(sub)) {
IGRAPH_ERROR("Cannot subtract directed and undirected graphs",
IGRAPH_EINVAL);
}
IGRAPH_VECTOR_INIT_FINALLY(&edge_ids, 0);
IGRAPH_VECTOR_INIT_FINALLY(&edges, 0);
IGRAPH_CHECK(igraph_inclist_init(orig, &inc_orig, IGRAPH_OUT));
IGRAPH_FINALLY(igraph_inclist_destroy, &inc_orig);
IGRAPH_CHECK(igraph_inclist_init(sub, &inc_sub, IGRAPH_OUT));
IGRAPH_FINALLY(igraph_inclist_destroy, &inc_sub);
smaller_nodes=no_of_nodes_orig > no_of_nodes_sub ?
no_of_nodes_sub : no_of_nodes_orig;
for (i=0; i<smaller_nodes; i++) {
long int n1, n2, e1, e2;
IGRAPH_ALLOW_INTERRUPTION();
nei1=igraph_inclist_get(&inc_orig, i);
nei2=igraph_inclist_get(&inc_sub, i);
n1=igraph_vector_size(nei1)-1;
n2=igraph_vector_size(nei2)-1;
while (n1>=0 && n2>=0) {
e1=(long int) VECTOR(*nei1)[n1];
e2=(long int) VECTOR(*nei2)[n2];
v1=IGRAPH_OTHER(orig, e1, i);
v2=IGRAPH_OTHER(sub, e2, i);
if (!directed && v1<i) {
n1--;
} else if (!directed && v2<i) {
n2--;
} else if (v1>v2) {
IGRAPH_CHECK(igraph_vector_push_back(&edge_ids, e1));
IGRAPH_CHECK(igraph_vector_push_back(&edges, i));
IGRAPH_CHECK(igraph_vector_push_back(&edges, v1));
n1--;
} else if (v2>v1) {
n2--;
} else {
n1--;
n2--;
}
}
/* Copy remaining edges */
while (n1>=0) {
e1=(long int) VECTOR(*nei1)[n1];
v1=IGRAPH_OTHER(orig, e1, i);
if (directed || v1 >= i) {
IGRAPH_CHECK(igraph_vector_push_back(&edge_ids, e1));
IGRAPH_CHECK(igraph_vector_push_back(&edges, i));
IGRAPH_CHECK(igraph_vector_push_back(&edges, v1));
}
n1--;
}
}
/* copy remaining edges, use the previous value of 'i' */
for (; i<no_of_nodes_orig; i++) {
long int n1, e1;
nei1=igraph_inclist_get(&inc_orig, i);
n1=igraph_vector_size(nei1)-1;
while (n1>=0) {
e1=(long int) VECTOR(*nei1)[n1];
v1=IGRAPH_OTHER(orig, e1, i);
if (directed || v1 >= i) {
IGRAPH_CHECK(igraph_vector_push_back(&edge_ids, e1));
IGRAPH_CHECK(igraph_vector_push_back(&edges, i));
IGRAPH_CHECK(igraph_vector_push_back(&edges, v1));
}
n1--;
}
}
igraph_inclist_destroy(&inc_sub);
igraph_inclist_destroy(&inc_orig);
IGRAPH_FINALLY_CLEAN(2);
IGRAPH_CHECK(igraph_create(res, &edges, (igraph_integer_t) no_of_nodes,
directed));
igraph_vector_destroy(&edges);
IGRAPH_FINALLY_CLEAN(1);
/* Attributes */
if (orig->attr) {
IGRAPH_I_ATTRIBUTE_DESTROY(res);
IGRAPH_I_ATTRIBUTE_COPY(res, orig, /*graph=*/1, /*vertex=*/1, /*edge=*/0);
IGRAPH_CHECK(igraph_i_attribute_permute_edges(orig, res, &edge_ids));
}
igraph_vector_destroy(&edge_ids);
IGRAPH_FINALLY_CLEAN(1);
return 0;
}
int igraph_to_directed(igraph_t *graph,
igraph_to_directed_t mode) {
if (mode != IGRAPH_TO_DIRECTED_ARBITRARY &&
mode != IGRAPH_TO_DIRECTED_MUTUAL) {
IGRAPH_ERROR("Cannot directed graph, invalid mode", IGRAPH_EINVAL);
}
if (igraph_is_directed(graph)) {
return 0;
}
if (mode==IGRAPH_TO_DIRECTED_ARBITRARY) {
igraph_t newgraph;
igraph_vector_t edges;
long int no_of_edges=igraph_ecount(graph);
long int no_of_nodes=igraph_vcount(graph);
long int size=no_of_edges*2;
IGRAPH_VECTOR_INIT_FINALLY(&edges, size);
IGRAPH_CHECK(igraph_get_edgelist(graph, &edges, 0));
IGRAPH_CHECK(igraph_create(&newgraph, &edges, no_of_nodes,
IGRAPH_DIRECTED));
IGRAPH_FINALLY(igraph_destroy, &newgraph);
igraph_vector_destroy(&edges);
IGRAPH_I_ATTRIBUTE_DESTROY(&newgraph);
IGRAPH_I_ATTRIBUTE_COPY(&newgraph, graph, 1,1,1);
IGRAPH_FINALLY_CLEAN(2);
igraph_destroy(graph);
*graph=newgraph;
} else if (mode==IGRAPH_TO_DIRECTED_MUTUAL) {
igraph_t newgraph;
igraph_vector_t edges;
igraph_vector_t index;
long int no_of_edges=igraph_ecount(graph);
long int no_of_nodes=igraph_vcount(graph);
long int size=no_of_edges*4;
long int i;
IGRAPH_VECTOR_INIT_FINALLY(&edges, 0);
IGRAPH_CHECK(igraph_vector_reserve(&edges, size));
IGRAPH_CHECK(igraph_get_edgelist(graph, &edges, 0));
IGRAPH_CHECK(igraph_vector_resize(&edges, no_of_edges*4));
IGRAPH_VECTOR_INIT_FINALLY(&index, no_of_edges*2);
for (i=0; i<no_of_edges; i++) {
VECTOR(edges)[no_of_edges*2+i*2] =VECTOR(edges)[i*2+1];
VECTOR(edges)[no_of_edges*2+i*2+1]=VECTOR(edges)[i*2];
VECTOR(index)[i] = VECTOR(index)[no_of_edges+i] = i+1;
}
IGRAPH_CHECK(igraph_create(&newgraph, &edges, no_of_nodes,
IGRAPH_DIRECTED));
IGRAPH_FINALLY(igraph_destroy, &newgraph);
IGRAPH_I_ATTRIBUTE_DESTROY(&newgraph);
IGRAPH_I_ATTRIBUTE_COPY(&newgraph, graph, 1,1,1);
IGRAPH_CHECK(igraph_i_attribute_permute_edges(&newgraph, &index));
igraph_vector_destroy(&index);
igraph_vector_destroy(&edges);
igraph_destroy(graph);
IGRAPH_FINALLY_CLEAN(3);
*graph=newgraph;
}
return 0;
}