TheAlgorithms/C-Sharp · error · InvalidOperationException

Edge weight cannot be zero.

Error message

Edge weight cannot be zero.

What it means

AddEdge rejects edges whose weight is exactly 0.0 via ThrowIfWeightZero, because 0.0 is used internally as the sentinel meaning 'no edge exists' in the weight matrix. A zero weight is therefore indistinguishable from a missing edge and is explicitly forbidden.

Solutions

1. Use a non-zero weight (e.g. 1.0 for unweighted semantics).
2. Guard the call: only add the edge when the weight is not 0.0.
3. If a zero-cost edge is genuinely needed, shift weights (e.g. add 1 to all) or use a different graph structure.

Example fix

// before
graph.AddEdge(a, b, weightB - weightA); // both equal -> 0.0 -> throws
// after
var w = weightB - weightA;
if (w != 0) graph.AddEdge(a, b, w);

static bool IsValidEdgeWeight(double w) => !w.Equals(0.0d);
// call: if (!IsValidEdgeWeight(w)) throw new ArgumentException("zero weight");

static bool IsNonZeroWeight(double w) => !w.Equals(0.0d);

try { graph.AddEdge(u, v, w); }
catch (InvalidOperationException ex) when (ex.Message == "Edge weight cannot be zero.") { /* skip or remap weight */ }

When it happens

Trigger: graph.AddEdge(v1, v2, 0.0) or AddEdge with a computed weight that evaluates to 0.0 (e.g. multiplying by zero, subtracting equal values).

Common situations: Modeling unweighted graphs with weight 0 instead of 1, computing weights as differences that cancel to zero, or deserializing edge lists where missing weights default to 0.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Graph capacity should always be a non-negative integer.
• Invalid parameter settings for Ascon Hash
• Cash flows list cannot be empty
• Graph contains a negative weight cycle.
• Matrix must be symmetric!

AI-assisted analysis of TheAlgorithms/C-Sharp@96e2905cab (2026-09-13). Data as JSON: /api/errors/4ac14f16683e5174. Report an issue: GitHub.

Appendix: source

Thrown at DataStructures/Graph/DirectedWeightedGraph.cs:206

            return adjacencyMatrix[startVertex.Index, endVertex.Index];
        }

        return 0;
    }

    private static void ThrowIfNegativeCapacity(int capacity)
    {
        if (capacity < 0)
        {
            throw new InvalidOperationException("Graph capacity should always be a non-negative integer.");
        }
    }

    private static void ThrowIfWeightZero(double weight)
    {
        if (weight.Equals(0.0d))
        {
            throw new InvalidOperationException("Edge weight cannot be zero.");
        }
    }

    private static void ThrowIfEdgeExists(double currentEdgeWeight)
    {
        if (!currentEdgeWeight.Equals(0.0d))
        {
            throw new InvalidOperationException($"Vertex already exists: {currentEdgeWeight}");
        }
    }

    private void ThrowIfOverflow()
    {
        if (Count == capacity)
        {
            throw new InvalidOperationException("Graph overflow.");
        }
    }

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