TheAlgorithms/Java · error · IllegalArgumentException

The input matrix cannot be empty

Error message

The input matrix cannot be empty

What it means

Thrown by QRDecomposition.validateInputMatrix when matrix.length == 0, i.e., the outer array exists but contains zero rows. QR decomposition operates on row/column data, so an empty matrix (0x0) has no diagonal to iterate over and no vectors to normalize. The check runs after the null check and before row validation.

Solutions

1. Verify the data source actually contains rows before building the double[][].
2. If an empty matrix is a legitimate case in your domain, branch around the call instead of passing it through.
3. Log the matrix dimensions immediately before the call to confirm row count.

Example fix

// before
List<double[]> rows = readRows(file);
double[][] m = rows.toArray(new double[0][]);
QRDecomposition.decompose(m);

// after
List<double[]> rows = readRows(file);
if (rows.isEmpty()) {
    throw new IllegalStateException("Input file contained no matrix rows");
double[][] m = rows.toArray(new double[0][]);
QRDecomposition.decompose(m);

if (matrix == null || matrix.length == 0) {
    throw new IllegalStateException("QR decomposition needs a non-empty matrix");
}

static boolean isNonEmptyMatrix(double[][] m) {
    return m != null && m.length > 0;
}

When it happens

Trigger: Passing new double[0][], a freshly allocated empty matrix from a constructor, or a filtered/collected matrix whose source produced no rows (e.g., an empty CSV file parsed into rows).

Common situations: Empty input dataset, an upstream filter that removed all rows, a test fixture that builds a matrix from an empty list via toArray(new double[0][]), or a default-initialized matrix before data is appended.

Related errors

• The input matrix cannot be empty
• The input matrix cannot be jagged
• The input matrix cannot be jagged
• The input matrix cannot be null
• The input matrix cannot be null

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/7e02c37507492051. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/com/thealgorithms/matrix/QRDecomposition.java:121

    private static double[] scalarMultiply(double[] v, double scalar) {
        double[] result = new double[v.length];
        for (int i = 0; i < v.length; i++) {
            result[i] = v[i] * scalar;
        }
        return result;
    }

    private static double norm(double[] v) {
        return Math.sqrt(dotProduct(v, v));
    }

    private static void validateInputMatrix(double[][] matrix) {
        if (matrix == null) {
            throw new IllegalArgumentException("The input matrix cannot be null");
        }
        if (matrix.length == 0) {
            throw new IllegalArgumentException("The input matrix cannot be empty");
        }
        if (!hasValidRows(matrix)) {
            throw new IllegalArgumentException("The input matrix cannot have null or empty rows");
        }
        if (isJaggedMatrix(matrix)) {
            throw new IllegalArgumentException("The input matrix cannot be jagged");
        }
    }

    private static boolean hasValidRows(double[][] matrix) {
        for (double[] row : matrix) {
            if (row == null || row.length == 0) {
                return false;
            }
        }
        return true;
    }

View on GitHub (pinned to fdfb9a395b)