[NUMBERS-180] Gamma ratio and delta ratio

• Type: New Feature
• Status: Closed
• Priority: Minor
• Resolution: Implemented
• Affects Version/s: 1.1
• Fix Version/s: 1.1
• Component/s: gamma
• Assignee: Unassigned
• Reporter: Alex Herbert
• Created: 20/Dec/21 22:43
• Updated: 01/Nov/22 11:00
• Resolved: 23/Dec/21 21:44

Description

The recently ported gamma functions from the Boost C++ library contain a method for computing a ratio of gamma functions:

gamma_ratio(a, b) = gamma(a) / gamma(b)

gamma_delta_ratio(a, delta) = gamma(a) / gamma(a + delta)

This method is required for part of the Boost C++ implementation of the RegularizedBeta function.

It has an application in Commons Statistics for computing the mean and variance of the Nakagami distribution.

Potential API:

// Added to the existing Gamma class
Gamma.ratio(a, b)
Gamma.delta_ratio(a, delta)

// New class
GammaRatio.value(a, b)
GammaRatio.delta(a, delta)