[jgrapht-users] Usage question

[David J. <djo...@gm...>]

Hi everyone,

Thank you in advance.

i am trying to understand how to use this library to accomplish what I
believe to be a basic task, but i am completely lost without some tutorials.

I am loading a graph of nodes and edges (tables and relationships), and
trying to pull back the shortest path for navigating from a beginning node
to a terminating node. I see Dijkstra's least-cost algorithm is built into
the CapacityScalingMinimumCostFlow class, so I believe this is the correct
component to be using to navigate the graph.

My difficulty is that the entirety of the library documentation appears to
be written for the mathematician, so I don't speak the jargon, and have not
been able to leverage any pre-existing code samples to understand the class
and its setup requirements.

Assuming I have built the graph correctly from the backing datastore, I
expected that this should have navigated the graph and returned the shorted
path in the flow variable for unmarshalling. However, it fails with the not
very informative o the lay person message "Total node supply isn't equal to
0".  Any hints, tutorial references, or sample code would be greatly
appreciated. I suspect that I don't understand the nodeSupplies() function.

Thank you in advance,

*Code Snip:*


private void findLeastCostPath(Graph<TableMetadata,
ColumnMetadataGraphEdge> graph, TableMetadata identityTable,
Map<Long, TableMetadata> tablesToLink) {

// return +1 for origin, -1 for target, 0 for anything intermediate
Function<TableMetadata, Integer> nodeSupplies = (TableMetadata t) -> {
if (t == identityTable) {
return 1;
} else if (tablesToLink.containsKey(t.getId())) {
return -1;
} else {
return 0;
}
};

Function<ColumnMetadataGraphEdge, Integer> arcCapacityLowerBounds =
(ColumnMetadataGraphEdge t) -> {
return 0;
};

Function<ColumnMetadataGraphEdge, Integer> arcCapacityUpperBounds =
(ColumnMetadataGraphEdge t) -> {
return CapacityScalingMinimumCostFlow.CAP_INF;
};

MinimumCostFlowProblem<TableMetadata, ColumnMetadataGraphEdge> flowProblem
= new MinimumCostFlowProblemImpl<TableMetadata, ColumnMetadataGraphEdge>(
graph, nodeSupplies, arcCapacityLowerBounds, arcCapacityUpperBounds);

CapacityScalingMinimumCostFlow<TableMetadata, ColumnMetadataGraphEdge>
minCostflow = new CapacityScalingMinimumCostFlow<>();
MinimumCostFlow<ColumnMetadataGraphEdge> flow =
minCostflow.getMinimumCostFlow(flowProblem);

logger.debug(flow.getFlowMap().toString());

}