oximation itself uses algorithm (4.1) of [2]_.

    Parameters
    ----------
    A : (N, N) array_like
        Matrix whose fractional power to evaluate.
    t : float
        Fractional power between -1 and 1 exclusive.

    Returns
    -------
    X : (N, N) array_like
        The fractional power of the matrix.

    References
    ----------
    .. [1] Nicholas J. Higham and Lijing Lin (2013)
           "An Improved Schur-Pade Algorithm for Fractional Powers
           of a Matrix and their Frechet Derivatives."

    .. [2] Nicholas J. Higham and Lijing lin (2011)
           "A Schur-Pade Algorithm for Fractional Powers of a Matrix."
           SIAM Journal on Matrix Analysis and Applications,
           32 (3). pp. 1056-1078. ISSN 0895-4798

    r!