/**
* Eliminate cycles for origin_id in the graph. Start searching at next_id and
* work recursively. Also "summarize" paths: Add up the flows along parallel
* paths in one.
* @param path Paths checked in parent calls to this method.
* @param origin_id Origin of the paths to be checked.
* @param next_id Next node to be checked.
* @return If any cycles have been found and eliminated.
*/
bool MCF1stPass::EliminateCycles(PathVector &path, NodeID origin_id, NodeID next_id)
{
static Path *invalid_path = new Path(INVALID_NODE, true);
Path *at_next_pos = path[next_id];
/* this node has already been searched */
if (at_next_pos == invalid_path) return false;
if (at_next_pos == NULL) {
/* Summarize paths; add up the paths with the same source and next hop
* in one path each. */
PathList &paths = this->job[next_id].Paths();
PathViaMap next_hops;
for (PathList::iterator i = paths.begin(); i != paths.end(); ++i) {
Path *new_child = *i;
if (new_child->GetOrigin() == origin_id) {
PathViaMap::iterator via_it = next_hops.find(new_child->GetNode());
if (via_it == next_hops.end()) {
next_hops[new_child->GetNode()] = new_child;
} else {
Path *child = via_it->second;
uint new_flow = new_child->GetFlow();
child->AddFlow(new_flow);
new_child->ReduceFlow(new_flow);
}
}
}
bool found = false;
/* Search the next hops for nodes we have already visited */
for (PathViaMap::iterator via_it = next_hops.begin();
via_it != next_hops.end(); ++via_it) {
Path *child = via_it->second;
if (child->GetFlow() > 0) {
/* Push one child into the path vector and search this child's
* children. */
path[next_id] = child;
found = this->EliminateCycles(path, origin_id, child->GetNode()) || found;
}
}
/* All paths departing from this node have been searched. Mark as
* resolved if no cycles found. If cycles were found further cycles
* could be found in this branch, thus it has to be searched again next
* time we spot it.
*/
path[next_id] = found ? NULL : invalid_path;
return found;
}
/* This node has already been visited => we have a cycle.
* Backtrack to find the exact flow. */
uint flow = this->FindCycleFlow(path, at_next_pos);
if (flow > 0) {
this->EliminateCycle(path, at_next_pos, flow);
return true;
}
return false;
}
/**
* Map the paths generated by the MCF solver into flows associated with nodes.
* @param component the link graph component to be used.
*/
void FlowMapper::Run(LinkGraphJob &job) const
{
for (NodeID node_id = 0; node_id < job.Size(); ++node_id) {
Node prev_node = job[node_id];
StationID prev = prev_node.Station();
PathList &paths = prev_node.Paths();
for (PathList::iterator i = paths.begin(); i != paths.end(); ++i) {
Path *path = *i;
uint flow = path->GetFlow();
if (flow == 0) break;
Node node = job[path->GetNode()];
StationID via = node.Station();
StationID origin = job[path->GetOrigin()].Station();
assert(prev != via && via != origin);
/* Mark all of the flow for local consumption at "first". */
node.Flows().AddFlow(origin, via, flow);
if (prev != origin) {
/* Pass some of the flow marked for local consumption at "prev" on
* to this node. */
prev_node.Flows().PassOnFlow(origin, via, flow);
} else {
/* Prev node is origin. Simply add flow. */
prev_node.Flows().AddFlow(origin, via, flow);
}
}
}
for (NodeID node_id = 0; node_id < job.Size(); ++node_id) {
/* Remove local consumption shares marked as invalid. */
Node node = job[node_id];
FlowStatMap &flows = node.Flows();
flows.FinalizeLocalConsumption(node.Station());
if (this->scale) {
/* Scale by time the graph has been running without being compressed. */
uint runtime = job.JoinDate() - job.Settings().recalc_time - job.LastCompression();
for (FlowStatMap::iterator i = flows.begin(); i != flows.end(); ++i) {
i->second.ScaleToMonthly(runtime);
}
}
/* Clear paths. */
PathList &paths = node.Paths();
for (PathList::iterator i = paths.begin(); i != paths.end(); ++i) {
delete *i;
}
paths.clear();
}
}
/**
* Clean up paths that lead nowhere and the root path.
* @param source_id ID of the root node.
* @param paths Paths to be cleaned up.
*/
void MultiCommodityFlow::CleanupPaths(NodeID source_id, PathVector &paths)
{
Path *source = paths[source_id];
paths[source_id] = NULL;
for (PathVector::iterator i = paths.begin(); i != paths.end(); ++i) {
Path *path = *i;
if (path == NULL) continue;
if (path->GetParent() == source) path->Detach();
while (path != source && path != NULL && path->GetFlow() == 0) {
Path *parent = path->GetParent();
path->Detach();
if (path->GetNumChildren() == 0) {
paths[path->GetNode()] = NULL;
delete path;
}
path = parent;
}
}
delete source;
paths.clear();
}