TheAlgorithms/C-Sharp · error · ArgumentException

Dot product arguments must have same dimension

Error message

Dot product arguments must have same dimension

What it means

VectorExtensions.Dot computes the dot product of two double[] vectors, which is only defined for vectors of equal length. When lhs.Length != rhs.Length it throws ArgumentException before summing, because element-wise pairing is impossible.

Solutions

1. Validate lhs.Length == rhs.Length before calling Dot
2. Align vector dimensions upstream (pad, truncate, or regenerate one vector)
3. Catch ArgumentException where vector length depends on external data and handle mismatch explicitly

Example fix

// before
var score = embedding.Dot(query); // lengths 384 vs 768 -> throws
// after
if (embedding.Length != query.Length)
{
    throw new ArgumentException($"Vector length mismatch: {embedding.Length} vs {query.Length}.");
}
var score = embedding.Dot(query);

if (lhs.Length != rhs.Length)
    throw new ArgumentException($"Dot product needs equal lengths: {lhs.Length} vs {rhs.Length}.");
var d = lhs.Dot(rhs);

try { var d = lhs.Dot(rhs); }
catch (ArgumentException) { /* handle embedding-dimension mismatch, e.g. re-embed inputs */ }

When it happens

Trigger: Calling lhs.Dot(rhs) with arrays of different lengths, e.g. a 3-element direction vector dotted with a 4-element feature vector; also reachable indirectly via Magnitude when a caller supplies a wrong-length comparison vector.

Common situations: Similarity/cosine computations over differently sized embeddings (e.g. changed model dimension); passing weights arrays of stale length after a config change; mixing sparse-representation length with dense length.

Related errors

• The width of a first operand should match the height of a…
• Dimensions of matrices must be the same
• The column vector should have only 1 element in width.
• The length of the start vector doesn't equal the size of…
• Both points should have the same dimensionality

AI-assisted analysis of TheAlgorithms/C-Sharp@96e2905cab (2026-09-13). Data as JSON: /api/errors/3798897b5abae611. Report an issue: GitHub.

Appendix: source

Thrown at Utilities/Extensions/VectorExtensions.cs:52

                result[i, j] = lhs[i] * rhs[j];
            }
        }

        return result;
    }

    /// <summary>
    ///     Computes the dot product of two vectors.
    /// </summary>
    /// <param name="lhs">The LHS vector.</param>
    /// <param name="rhs">The RHS vector.</param>
    /// <returns>The dot product of the two vector.</returns>
    /// <exception cref="ArgumentException">Dimensions of vectors do not match.</exception>
    public static double Dot(this double[] lhs, double[] rhs)
    {
        if (lhs.Length != rhs.Length)
        {
            throw new ArgumentException("Dot product arguments must have same dimension");
        }

        double result = 0;
        for (var i = 0; i < lhs.Length; i++)
        {
            result += lhs[i] * rhs[i];
        }

        return result;
    }

    /// <summary>
    ///     Computes the magnitude of a vector.
    /// </summary>
    /// <param name="vector">The vector.</param>
    /// <returns>The magnitude.</returns>
    public static double Magnitude(this double[] vector)
    {

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