[
https://issues.apache.org/jira/browse/NUMBERS-174?focusedWorklogId=687441&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-687441
]
ASF GitHub Bot logged work on NUMBERS-174:
------------------------------------------
Author: ASF GitHub Bot
Created on: 29/Nov/21 17:00
Start Date: 29/Nov/21 17:00
Worklog Time Spent: 10m
Work Description: asfgit merged pull request #110:
URL: https://github.com/apache/commons-numbers/pull/110
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
Issue Time Tracking
-------------------
Worklog Id: (was: 687441)
Remaining Estimate: 0h
Time Spent: 10m
> Update Gamma functions using the Boost implementation
> -----------------------------------------------------
>
> Key: NUMBERS-174
> URL: https://issues.apache.org/jira/browse/NUMBERS-174
> Project: Commons Numbers
> Issue Type: Improvement
> Components: gamma
> Affects Versions: 1.0
> Reporter: Alex Herbert
> Assignee: Alex Herbert
> Priority: Major
> Fix For: 1.1
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> The current regularised incomplete gamma functions for P and Q compute using
> a series representation for all input. This method is not robust to extreme
> arguments.
> The Gamma functions are used in Commons Statistics in the Gamma and Poisson
> distributions.
> Large values of the mean in the Poisson distribution have low
> precision for the CDF. The distribution also has a configurable
> threshold for convergence of the gamma function evaluation
> (STATISTICS-38). Ideally this implementation detail should be
> removed from the API.
> The Gamma distribution has a function switch based on a threshold to
> compute the PDF. This threshold results in incorrect values for
> certain parameters (STATISTICS-39).
> The function switch in the Gamma distribution is based on the
> documentation for the Boost gamma functions [1]. However it does not
> implement all the suggested optimisations detailed in the most recent
> Boost documentation. This includes avoiding using the converging
> series of the gamma function when the convergence is slow or unstable,
> i.e. addresses the need for a configurable convergence threshold in
> the Poisson distribution.
> One part of the evaluation of the incomplete gamma functions require
> accuracy in the leading term:
> {noformat}
> x^a exp(-x) / gamma(a) = exp(a log(x) - x - loggamma(a){noformat}
> When x and a are large then using logs to compute this leads to
> cancellation. Use of logs to compute this term is done in the current
> implementation in numbers for RegularizedGamma P and Q. It is the
> source of low precision for the CDF for the Poisson distribution when
> the mean is large.
> I propose to port the Boost gamma functions to numbers. This will be a
> process similar to the recent port of the error functions to the same
> package in numbers. These functions improved both accuracy and
> speed over the existing implementation. Once the gamma functions are
> ported a comparison can be made between the existing and new
> implementations.
> [1]
> [https://www.boost.org/doc/libs/1_77_0/libs/math/doc/html/math_toolkit/sf_gamma/igamma.html]
--
This message was sent by Atlassian Jira
(v8.20.1#820001)
