Example #1
0
/**
 * 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;
}
Example #2
0
/**
 * 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();
	}
}
Example #3
0
/**
 * 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();
}