Log Minus Digamma Function
The difference between the log and digamma functions.
logmdigamma(x)
x |
numeric vector or array of positive values. Negative or zero values will return |
digamma(x) is asymptotically equivalent to log(x). logmdigamma(x) computes log(x) - digamma(x) without subtractive cancellation for large x.
Gordon Smyth
Abramowitz, M., and Stegun, I. A. (1970). Handbook of mathematical functions. Dover, New York.
log(10^15) - digamma(10^15) # returns 0 logmdigamma(10^15) # returns value correct to 15 figures
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