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Added Dijkstra version for digraph with edges weights #319

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Added Dijkstra version for digraph with edges weights #319

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3 changes: 2 additions & 1 deletion gap/oper.gd
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Original file line number Diff line number Diff line change
Expand Up @@ -98,7 +98,8 @@ DeclareOperation("DigraphDijkstra",
[IsDigraph, IsPosInt]);
DeclareOperation("DigraphDijkstra",
[IsDigraph, IsPosInt, IsPosInt]);

DeclareOperation("DigraphDijkstraSTWeights",
[IsDigraph, IsPosInt, IsPosInt, IsList]);
DeclareOperation("DigraphConnectedComponent", [IsDigraph, IsPosInt]);
DeclareOperation("DigraphStronglyConnectedComponent", [IsDigraph, IsPosInt]);
DeclareOperation("DigraphPath", [IsDigraph, IsPosInt, IsPosInt]);
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31 changes: 31 additions & 0 deletions gap/oper.gi
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Expand Up @@ -1365,6 +1365,37 @@ InstallMethod(DigraphDijkstra, "for a digraph, and a vertex",
[IsDigraph, IsPosInt],
{digraph, source} -> DIGRAPHS_DijkstraST(digraph, source, fail));
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{digraph, source} -> DIGRAPHS_DijkstraST(digraph, source, fail))

would become

{digraph, source} -> DIGRAPHS_DijkstraST(digraph, source, fail, {u, v} -> 1))


InstallMethod(DigraphDijkstraSTWeights, "for a digraph, a vertex, a vertex, and a list of weights",
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I suggest using your new version DigraphDijkstraSTWeights as the code of DIGRAPHS_DijkstraST, with one change: the argument weights could be a function like:

weights := function(u, v)
  return list_of_weights[u][v];
end;

if a list of weights is given, and if no list of weights is given then we could do:

weights := function(u, v)
  return 1;
end;

[IsDigraph, IsPosInt, IsPosInt, IsList],
function(digraph, source, target, weights)
local dist, prev, queue, u, v, alt;
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Check that the weights have the same "shape" as OutNeighbours(digraph)


dist := [];
prev := [];
queue := BinaryHeap({x, y} -> x[1] < y[1]);

for v in DigraphVertices(digraph) do
dist[v] := infinity;
prev[v] := -1;
od;

dist[source] := 0;
Push(queue, [0, source]);

while not IsEmpty(queue) do
u := Pop(queue);
u := u[2];
for v in OutNeighbours(digraph)[u] do
alt := dist[u] + weights[u][v];
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would become weights(u, v) instead of weights[u][v]

if alt < dist[v] then
dist[v] := alt; prev[v] := u;
Push(queue, [dist[v], v]);
fi;
od;
od;
return [dist, prev];
end);

InstallMethod(IteratorOfPaths,
"for a digraph by out-neighbours and two pos ints",
[IsDigraphByOutNeighboursRep, IsPosInt, IsPosInt],
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