RosettaCodeData/Task/Resistor-mesh/Mathematica/resistor-mesh-2.math

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graphresistor[g_, a_, b_] :=
LinearSolve[
SparseArray[{{a, a} -> 1, {i_, i_} :> Length@AdjacencyList[g, i],
Alternatives @@ Join[#, Reverse /@ #] &[
List @@@ EdgeList[VertexDelete[g, a]]] -> -1}, {VertexCount[
g], VertexCount[g]}], SparseArray[b -> 1, VertexCount[g]]][[b]];
N[graphresistor[GridGraph[{10, 10}], 12, 77], 40]