loggamma

Use the loggamma function in APL to compute the natural logarithm of the absolute value of the gamma function. This is equivalent to log(abs(gamma(x))) but avoids the numeric overflow that occurs when gamma(x) itself becomes too large to represent as a floating-point number.

loggamma is useful when you work with large inputs to the gamma function in statistical calculations, such as log-likelihood computations, Bayesian modeling, or custom anomaly scoring. Use it whenever gamma(x) would overflow to infinity.

Usage

Syntax

loggamma(x)

Parameters

Returns

The natural logarithm of the absolute value of the gamma function of x.

Example

Use loggamma to compute the log-gamma value of a duration in seconds without risking numeric overflow.

Query

['sample-http-logs']
| where req_duration_ms > 0
| extend duration_s = req_duration_ms / 1000.0
| extend loggamma_val = loggamma(duration_s)
| project _time, id, req_duration_ms, loggamma_val

Output

List of related functions

• gamma: Returns the gamma function directly. Use it for small inputs where overflow isn't a concern.
• log: Returns the natural logarithm. Use it for general log-transformation without the gamma relationship.
• exp: Returns e^x. Use it to exponentiate loggamma results back to the original gamma scale when the values are small enough.
• isfinite: Returns whether a value is finite. Use it to verify that loggamma results are valid for downstream calculations.
• abs: Returns the absolute value. Note that loggamma(x) equals log(abs(gamma(x))), so abs is implicitly applied to gamma(x) before the log.

Other query languages