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The difference between the log and digamma functions.
log
digamma
logmdigamma(x)
numeric vector or array of positive values. Negative or zero values will return NA.
NA
Gordon Smyth
digamma(x) is asymptotically equivalent to log(x). logmdigamma(x) computes log(x) - digamma(x) without subtractive cancellation for large x.
digamma(x)
log(x)
log(x) - digamma(x)
x
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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