digamma(z)
bdVector
.
z
.
The digamma function is the derivative of the log gamma function
(Abramowitz and Stegun (1965, p. 258).
The Spotfire S+
digamma
function is taken
from the
MASS
library of
Venables and Ripley (1997).
Abramowitz, M., and Stegun, I. A. (Eds.). (1965).
Handbook of Mathematical Functions.
New York: Dover.
Venables, W. N. and Ripley, B. D. (1997).
Modern Applied Statistics with S-PLUS, Second Ed.
New York: Springer.
digamma(5) # Gives: 1.506118 # Numerical derivatives using log gamma and gamma functions (lgamma(5+1.0e-6)-lgamma(5))/1.0e-6 # Gives: 1.506118 (gamma(5+1.0e-6)-gamma(5))/1.0e-6/gamma(5) # Gives: 1.506119