void OrientedGraph::permute(const Permutation& a)
/*
This function permutes the graph according to the permutation a, according
to the usual rule : the edges of a(x) should be the image under a of the
edge set of x.
As usual, permuting values is easy : it is enough to apply a to the
elements in the various edgelists. Permuting ranges is trickier, because
it involves a^-1.
It is assumed of course that a holds a permutation of size size().
*/
{
static BitMap b(0);
static EdgeList e_buf(0);
/* permute values */
for (SetElt x = 0; x < size(); ++x) {
EdgeList& e = d_edge[x];
for (Ulong j = 0; j < e.size(); ++j) {
e[j] = a[e[j]];
}
}
/* permute ranges */
b.setSize(size());
b.reset();
for (SetElt x = 0; x < size(); ++x) {
if (b.getBit(x))
continue;
if (a[x] == x) { /* fixed point */
b.setBit(x);
continue;
}
for (SetElt y = a[x]; y != x; y = a[y]) {
/* back up values for y */
e_buf.shallowCopy(d_edge[y]);
/* put values for x in y */
d_edge[y].shallowCopy(d_edge[x]);
/* store backup values in x */
d_edge[x].shallowCopy(e_buf);
/* set bit */
b.setBit(y);
}
b.setBit(x);
}
}
