[Help-gsl] ln of gamma function for negative arguments

[Marc Normandin]

Hello,

I require the computation of ln of the gamma function for all negative 
non-integer values. The reflection formula can be used for half of the negative 
non-integers along with the log since for half the values will be positive. 
However, I would like to obtain a value for the other half. I'm using the ln of 
gamma as an intermediate step after which I raise the result with an 
exponential, so that ultimately I am not after the actual value of ln gamma 
itself. I am open to any methods that work.

At the current time the only way that I've found to compute the ln of gamma for 
negative non-integer values is to treat the argument as a complex number z = -x 
+ 0i and then use Ln(z) = ln(|z|) + iPI, for the term involving the sin from 
the relfection formula.

I'd appreciate help and suggestions.

Thanks,
   Marc.