loggamma

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#

Name	Type	Required	Description
`x`	real	Yes	The input value. Must not be zero or a negative integer.

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

Run in Playground

Output

_time	id	req_duration_ms	loggamma_val
2024-11-14 10:00:00	user-1	1000.0	0.0000
2024-11-14 10:01:00	user-2	2000.0	0.0000
2024-11-14 10:02:00	user-3	10000.0	16.1181

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#

Splunk SPL users

Splunk SPL doesn't include a built-in loggamma() function. You typically implement it using external libraries or the Machine Learning Toolkit.

Splunk example

| eval loggamma_val = null()

APL equivalent

['sample-http-logs']
| extend loggamma_val = loggamma(x)

ANSI SQL users

Standard SQL does not define a LOGGAMMA() function. You need to implement it in application code or through database-specific extensions.

SQL example

-- No standard SQL equivalent; use application code
SELECT NULL AS loggamma_val FROM logs