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These routines compute the Pochhammer symbol (a)_x = \Gamma(a + x)/\Gamma(a), subject to a and a+x not being negative integers or zero. The Pochhammer symbol is also known as the Apell symbol and sometimes written as (a,x).
These routines compute the logarithm of the Pochhammer symbol, \log((a)_x) = \log(\Gamma(a + x)/\Gamma(a)) for a > 0, a+x > 0.
These routines compute the sign of the Pochhammer symbol and the logarithm of its magnitude. The computed parameters are result = \log(|(a)_x|) and sgn = \sgn((a)_x) where (a)_x = \Gamma(a + x)/\Gamma(a), subject to a, a+x not being negative integers or zero.