Hi everyone,

Apologies for this being a long one. I am working with the bellman ford algorithm from lightgraphs.jl but having an issue with some of my functions. My intension behind this is to have a general mapping function that goes over all edges in a graph and applies a function. Many algorithms loop over edges and apply calculations so a generic edgeMap function could be useful.

My edgeMap function:

```
function edgeMapSparse(g::AbstractGraph,f::Function,active,x...)
@threads for u in vertices(g)
if active[u] == true
for v in outneighbors(g,u)
f(u,v,g,x...)
end
end
end
end
```

Bellman ford algorithm

```
function bf_compute(graph,distance,distance_max,predecessor,no_changes,new_active,active)
for v in vertices(graph)
if active[v] == true
for u in outneighbors(graph, v)
relax_dist = distance_max[v,u] + distance[v]
if distance[u] > relax_dist
distance[u] = relax_dist
predecessor[u] = v
no_changes = false
new_active[u] = true
end
end
end
end
return new_active,no_changes
end
function b_ford(graph::AbstractGraph{<:Integer},source::AbstractVector{<:Integer},distance_max::AbstractMatrix=weights(graph))
if has_negative_edge_cycle(graph) == true
error("Graph contains a negative edge cycle")
end
n = nv(graph)
active = falses(n) #BitArray that holds actie edges (edge becomes active when it is visited)
active[source] .= true
predecessor = zeros(Integer, n)
int_max = typemax(Int64)
distance = fill(int_max, n) #initialize the distance to all vertices to maximum of Int64
distance[source] .= 0 #the distance from the source to itself (the source) is 0
no_changes = false #Array that tracks if
new_active = falses(n) #BitArray that will be used to track if an edge is newly active
for _ in 1:n
no_changes = true
new_active .= false
edgeMapSparse(graph,bf_compute,distance,distance_max,predecessor,no_changes,new_active)
no_changes && break
active, new_active = new_active, active
end
return predecessor, distance
end
```

When I try some simple output from the following code I get the wrong answer. This is because I need to return the variables â€śnew_activeâ€ť & â€śno_changesâ€ť. My question is whether there is a way to return these values without making the edgeMap non-generic?

```
g1 = SimpleDiGraph(4) #Create a directed graph with 4 nodes and add edges to each node
add_edge!(g1, 1, 2);
add_edge!(g1, 1, 3);
add_edge!(g1, 2, 4);
add_edge!(g1, 3, 1);
add_edge!(g1, 3, 2);
add_edge!(g1, 3, 4);
add_edge!(g1, 4, 3);
bf_g1 = b_ford(g1,[2])
#returns 0,0,0,0 & 9223372036854775807,0,9223372036854775807,9223372036854775807
#correct answer is 3,0,2,4 & 3,0,2,1.
```

I appreciate that this is a very long one and any help would be much appreciated.