TheAlgorithms/Go · error

index out of bounds

Error message

index out of bounds

What it means

Set(row, col, val) returns this error when the target coordinates are outside the matrix (negative or >= row/column count). The matrix is left unmodified. Note the message differs slightly from Get's ("out of bounds" vs "out of range").

Source

Thrown at math/matrix/matrix.go:76

	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 {
	if len(m.elements) == 0 {
		return 0
	}
	return len(m.elements[0])
}

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Validate 0 <= row < m.Rows() and 0 <= col < m.Columns() before Set.
2. Correct loop bounds (use i < rows, j < cols) and argument order.
3. Re-create the matrix with New(rows, cols, zero) if it is smaller than needed.

Example fix

// before
for i := 0; i <= 3; i++ { m.Set(i, 0, v) } // errors at i == 3

// after
for i := 0; i < m.Rows(); i++ { m.Set(i, 0, v) }

if r < 0 || r >= m.Rows() || c < 0 || c >= m.Columns() {
    return fmt.Errorf("cannot set (%d,%d) on %dx%d matrix", r, c, m.Rows(), m.Columns())
}
err := m.Set(r, c, v)

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

if err := m.Set(r, c, v); err != nil {
    return fmt.Errorf("set(%d,%d) failed: %w", r, c, err)
}

When it happens

Trigger: Calling Set with row >= m.rows, col >= m.columns, or negative values — e.g. Set(1,3,v) on a 3-column matrix, or any Set on an empty 0x0 matrix.

Common situations: Off-by-one fill loops (i <= size), writing to coordinates computed from another (larger) matrix, 1-based index habits, resizing logic that shrank the matrix but not the loop.

Related errors

• index out of range
• submatrix dimensions exceed matrix 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

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/c16ebce130e86ad4. Report an issue: GitHub.