def _B(self, x, a, b):
        """
        incomplete Beta function as described in Mamon&Lokas A13

        :param x:
        :param a:
        :param b:
        :return:
        """
        return special.betainc(a, b, x) * special.beta(a, b)
incomplete Beta function as described in Mamon&Lokas A13

        :param x:
        :param a:
        :param b:
        :return: