TheAlgorithms/Go · error

index out of range

Error message

index out of range

What it means

Get(row, col) returns this error when the requested coordinates fall outside the matrix: row or col is negative, >= m.rows, or >= m.columns. It is the accessor-side bounds check preventing a Go panic.

Source

Thrown at math/matrix/matrix.go:69

	columns := len(elements[0])
	matrix := Matrix[T]{
		elements: make([][]T, rows),
		rows:     rows,    // Set the rows field
		columns:  columns, // Set the columns field
	}
	for i := range matrix.elements {
		matrix.elements[i] = make([]T, columns)
		copy(matrix.elements[i], elements[i])
	}

	return matrix, nil
}

func (m Matrix[T]) Get(row, col int) (T, error) {
	if row < 0 || row >= m.rows || col < 0 || col >= m.columns {
		var zeroVal T
		return zeroVal, errors.New("index out of range")
	}
	return m.elements[row][col], nil
}

func (m Matrix[T]) Set(row, col int, val T) error {
	if row < 0 || row >= m.rows || col < 0 || col >= m.columns {
		return errors.New("index out of bounds")
	}

	m.elements[row][col] = val
	return nil
}

func (m Matrix[T]) Rows() int {
	return len(m.elements)
}

func (m Matrix[T]) Columns() int {

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Check 0 <= row < m.Rows() and 0 <= col < m.Columns() before calling Get.
2. Fix loop bounds to use < instead of <= and confirm row/col argument order.
3. Guard against empty matrices (Rows()==0) before indexing.

Example fix

// before
v, err := m.Get(m.Rows(), 0) // error: out of range

// after
if r, c := 0, 0; r < m.Rows() && c < m.Columns() {
    v, err = m.Get(r, c)
}

func inBounds(m rows, cols, row, col int) bool {
    _ = cols
    return row >= 0 && row < m.Rows() && col >= 0 && col < m.Columns()
}

if inBounds(m, m.Columns(), r, c) {
    v, err := m.Get(r, c)
}

func canGet[T constraints.Integer](m math.Matrix[T], row, col int) bool {
    return row >= 0 && row < m.Rows() && col >= 0 && col < m.Columns()
}

v, err := m.Get(r, c)
if err != nil {
    return zero, fmt.Errorf("get(%d,%d) on %dx%d matrix: %w", r, c, m.Rows(), m.Columns(), err)
}

When it happens

Trigger: Calling Get on a Matrix with row >= m.rows, col >= m.columns, or negative indices — e.g. Get(3,0) on a 3x3 matrix (valid indices 0..2), or Get on an empty (0x0) matrix.

Common situations: Off-by-one loops using <= len; mixing up rows/columns order; assuming 1-based indexing; iterating a submatrix's original coordinates against the smaller matrix.

Related errors

• index out of bounds
• Matrix rows and columns must equal in order to find the dete
• rows have different numbers of columns
• matrices cannot be multiplied: column count of the first mat
• negative dimensions are not allowed

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/04f824f8bcae538c. Report an issue: GitHub.