is_cyclic: determine which cells contain issues

[AquaPore]

Hi,

Thanks for this amazing software.

I am using the Wflow model and from the derived Local Drain Direction it is checking if there are issues in cyclic, by using is_cyclic . I am writing to determine if it may be possible to determine which cells are causing issues?

Many thanks for any help you may provide,
Joseph

    if is_cyclic(graph)
        error("""One or more cycles detected in flow graph.
            The provided local drainage direction map may be unsound.
            Verify that each active flow cell flows towards a pit.
            """)
    end

[henrik-wolf]

You should be able to run Graphs.simplecycles (or probably Graphs.simplecycles_iter if your graph is on the larger side) to get some idea about the cycles?

[Krastanov]

FYI, I converted this "issue" to a QnA "discussion"

[AquaPore]

@henrik-wolf @Krastanov

A great thanks for providing me with a quick answer,

I run the Wflow model by modifying the code as below and I get the following result: [[368]]

To assure that I interpret the result correctly, the issue is in the indices=368 , is that correct?

If this is the case then I need to convert indice ->[ iX, iY] -> [X_Coordinate, Y_Coordinate]

Many thanks for the great help you provided,
Joseph Pollacco

(A) RUN CODE (MODIFIED WFLOW)

"Convert a gridded drainage direction to a directed graph"
function flowgraph(ldd::AbstractVector, indices::AbstractVector, PCR_DIR::AbstractVector)
    # prepare a directed graph to be filled
    n = length(indices)
    graph = DiGraph(n)

    # loop over ldd, adding the edge to the downstream node
    for (from_node, from_index) in enumerate(indices)
        ldd_val = ldd[from_node]
        # skip pits to prevent cycles
        ldd_val == 5 && continue
        to_index = from_index + PCR_DIR[ldd_val]
        # find the node id of the downstream cell
        to_node = searchsortedfirst(indices, to_index)
        add_edge!(graph, from_node, to_node)
    end
    if is_cyclic(graph)

        println("simplecycles:")
        println( Graphs.simplecycles(graph))
        println("simplecycles_ter:")
        println(Graphs.simplecycles_iter(graph))
        
        error("""One or more cycles detected in flow graph.
            The provided local drainage direction map may be unsound.
            Verify that each active flow cell flows towards a pit.
            """)
    end
    return graph
end

(B) RESULTS

simplecycles:
[[368]]
simplecycles_ter:
[[368]]