What causes "negative dimensions are not allowed" in TheAlgorithms/Go?

Clamp offsets: if rowStart = 0.

negative dimensions are not allowed

Error message

negative dimensions are not allowed

What it means

SubMatrix returns this error when any of rowStart, colStart, numRows, numCols is negative. Negative coordinates or sizes are meaningless for an extraction window, so the call is rejected before any bounds math runs.

Solutions

Clamp offsets: if rowStart < 0 { rowStart = 0 } (same for colStart) and ensure numRows/numCols >= 0.
Validate all four arguments are >= 0 before calling SubMatrix.
Fix the computation that produced the negative value (order of operands in subtraction).

Example fix

// before
sub, err := m.SubMatrix(i-pad, j-pad, h, w) // error when i < pad

// after
rs, cs := max(0, i-pad), max(0, j-pad)
sub, err := m.SubMatrix(rs, cs, h, w)

Defensive patterns

Strategy: validation

Validate before calling

if rowStart < 0 || colStart < 0 || numRows < 0 || numCols < 0 {
    rowStart, colStart = max(rowStart, 0), max(colStart, 0)
    numRows, numCols = max(numRows, 0), max(numCols, 0)
}
sub, err := m.SubMatrix(rowStart, colStart, numRows, numCols)

Try / catch

sub, err := m.SubMatrix(rs, cs, nr, nc)
if err != nil {
    return Matrix{}, fmt.Errorf("submatrix(%d,%d,%d,%d): %w", rs, cs, nr, nc, err)
}

Prevention

Clamp computed offsets with max(0, x) before slicing.
Keep padding arithmetic explicit and tested near boundaries.
Distinguish start offsets from sizes in variable names.

When it happens

Trigger: Calling m.SubMatrix with a negative argument, e.g. SubMatrix(-1, 0, 2, 2) or SubMatrix(0, 0, -3, 3); computed offsets that underflow (start - padding < 0).

Common situations: Subtracting a padding/margin from an index without clamping to zero; loop variables that go negative near boundaries; swapped sign in a computed offset.

Related errors

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/9c2c4328f4d4c44d. Report an issue: GitHub.

Appendix: source

Thrown at math/matrix/submatrix.go:12

package matrix

import (
	"context"
	"errors"
	"sync"
)

// SubMatrix extracts a submatrix from the current matrix.
func (m Matrix[T]) SubMatrix(rowStart, colStart, numRows, numCols int) (Matrix[T], error) {
	if rowStart < 0 || colStart < 0 || numRows < 0 || numCols < 0 {
		return Matrix[T]{}, errors.New("negative dimensions are not allowed")
	}

	if rowStart+numRows > m.rows || colStart+numCols > m.columns {
		return Matrix[T]{}, errors.New("submatrix dimensions exceed matrix bounds")
	}

	var zeroVal T
	if numRows == 0 || numCols == 0 {
		return New(numRows, numCols, zeroVal), nil // Return an empty matrix
	}

	subMatrix := New(numRows, numCols, zeroVal)

	ctx, cancel := context.WithCancel(context.Background())
	defer cancel() // Make sure it's called to release resources even if no errors

	var wg sync.WaitGroup
	errCh := make(chan error, 1)

View on GitHub (pinned to 5ba447ec5f)