trigamma
==============================================

Purpose
----------------

Computes trigamma function.

Format
----------------
.. function:: y = trigamma(x)

    :param x: data
    :type x: MxN matrix or N-dimensional array

    :return y: trigamma.

    :rtype y: MxN matrix or N-dimensional array

Remarks
-------

The :func:`trigamma` function is the second derivative of the log of the gamma function with respect to its argument.