functions in gamma.i -

             beta(z,w)  
 
     returns the beta function gamma(z)gamma(w)/gamma(z+w)  

             bico(n,k)  
 
     returns the binomial coefficient n!/(k!(n-k)!) as a double.  

             erfc_nr(x)  
 
     returns the complementary error function 1-erf with fractional  
     error less than 1.2e-7 everywhere.  

             ln_gamma(z)  
 
     returns natural log of the gamma function.  
     Error is less than 1e-13 for real part of z>=1.  
     Use lngamma if you know that all z>=1, or if you don't care much about  
     accuracy for z<1.  

             lngamma(x)  
 
     returns natural log of the gamma function.  
     Error is less than 1e-13 for real part of x>=1.  
     Use ln_gamma if some x<1.