/**
* Push flow along a path and update the unsatisfied_demand of the associated
* edge.
* @param edge Edge whose ends the path connects.
* @param path End of the path the flow should be pushed on.
* @param accuracy Accuracy of the calculation.
* @param max_saturation If < UINT_MAX only push flow up to the given
* saturation, otherwise the path can be "overloaded".
*/
uint MultiCommodityFlow::PushFlow(Edge &edge, Path *path, uint accuracy,
uint max_saturation)
{
assert(edge.UnsatisfiedDemand() > 0);
uint flow = Clamp(edge.Demand() / accuracy, 1, edge.UnsatisfiedDemand());
flow = path->AddFlow(flow, this->job, max_saturation);
edge.SatisfyDemand(flow);
return flow;
}
/**
* Run the second pass of the MCF calculation which assigns all remaining
* demands to existing paths.
* @param job Link graph job to calculate.
*/
MCF2ndPass::MCF2ndPass(LinkGraphJob &job) : MultiCommodityFlow(job)
{
this->max_saturation = UINT_MAX; // disable artificial cap on saturation
PathVector paths;
uint size = job.Size();
uint accuracy = job.Settings().accuracy;
bool demand_left = true;
while (demand_left) {
demand_left = false;
for (NodeID source = 0; source < size; ++source) {
this->Dijkstra<CapacityAnnotation, FlowEdgeIterator>(source, paths);
for (NodeID dest = 0; dest < size; ++dest) {
Edge edge = this->job[source][dest];
Path *path = paths[dest];
if (edge.UnsatisfiedDemand() > 0 && path->GetFreeCapacity() > INT_MIN) {
this->PushFlow(edge, path, accuracy, UINT_MAX);
if (edge.UnsatisfiedDemand() > 0) demand_left = true;
}
}
this->CleanupPaths(source, paths);
}
}
}
/**
* Run the first pass of the MCF calculation.
* @param job Link graph job to calculate.
*/
MCF1stPass::MCF1stPass(LinkGraphJob &job) : MultiCommodityFlow(job)
{
PathVector paths;
uint size = job.Size();
uint accuracy = job.Settings().accuracy;
bool more_loops;
do {
more_loops = false;
for (NodeID source = 0; source < size; ++source) {
/* First saturate the shortest paths. */
this->Dijkstra<DistanceAnnotation, GraphEdgeIterator>(source, paths);
for (NodeID dest = 0; dest < size; ++dest) {
Edge edge = job[source][dest];
if (edge.UnsatisfiedDemand() > 0) {
Path *path = paths[dest];
assert(path != NULL);
/* Generally only allow paths that don't exceed the
* available capacity. But if no demand has been assigned
* yet, make an exception and allow any valid path *once*. */
if (path->GetFreeCapacity() > 0 && this->PushFlow(edge, path,
accuracy, this->max_saturation) > 0) {
/* If a path has been found there is a chance we can
* find more. */
more_loops = more_loops || (edge.UnsatisfiedDemand() > 0);
} else if (edge.UnsatisfiedDemand() == edge.Demand() &&
path->GetFreeCapacity() > INT_MIN) {
this->PushFlow(edge, path, accuracy, UINT_MAX);
}
}
}
this->CleanupPaths(source, paths);
}
} while (more_loops || this->EliminateCycles());
}