{{alias}}( out[, means] )
    Returns an accumulator function which incrementally computes an unbiased
    sample covariance matrix.

    If provided a data vector, the accumulator function returns an updated
    unbiased sample covariance matrix. If not provided a data vector, the
    accumulator function returns the current unbiased sample covariance matrix.

    Parameters
    ----------
    out: integer|ndarray
        Order of the covariance matrix or a square 2-dimensional ndarray for
        storing the covariance matrix.

    means: ndarray (optional)
        Known means.

    Returns
    -------
    acc: Function
        Accumulator function.

    Examples
    --------
    > var accumulator = {{alias}}( 2 );
    > var out = accumulator()
    <ndarray>
    > var buf = new {{alias:@stdlib/array/float64}}( 2 );
    > var shape = [ 2 ];
    > var strides = [ 1 ];
    > var v = {{alias:@stdlib/ndarray/ctor}}( 'float64', buf, shape, strides, 0, 'row-major' );
    > v.set( 0, 2.0 );
    > v.set( 1, 1.0 );
    > out = accumulator( v )
    <ndarray>
    > v.set( 0, -5.0 );
    > v.set( 1, 3.14 );
    > out = accumulator( v )
    <ndarray>
    > out = accumulator()
    <ndarray>

    See Also
    --------