Log Minus Digamma Function

The difference between the log and digamma functions.

logmdigamma(x)

Arguments

x

numeric vector or array of positive values. Negative or zero values will return NA.

Details

digamma(x) is asymptotically equivalent to log(x). logmdigamma(x) computes log(x) - digamma(x) without subtractive cancellation for large x.

Author

Gordon Smyth

References

Abramowitz, M., and Stegun, I. A. (1970). Handbook of mathematical functions. Dover, New York.

See also

digamma

Examples

log(10^15) - digamma(10^15) # returns 0
#> [1] 0
logmdigamma(10^15) # returns value correct to 15 figures
#> [1] 5e-16