--------
T : (N, N) array_like
    Upper triangular 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

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