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https://issues.apache.org/jira/browse/NUMBERS-209?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert resolved NUMBERS-209.
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Fix Version/s: 1.4
Assignee: Alex Herbert
Resolution: Fixed
Fixed in commit:
8ac25c90936d47a90b41126dffd0a0511094acf2
> Infinite loop for Trigamma function on large negative values
> ------------------------------------------------------------
>
> Key: NUMBERS-209
> URL: https://issues.apache.org/jira/browse/NUMBERS-209
> Project: Commons Numbers
> Issue Type: Bug
> Components: gamma
> Affects Versions: 1.3
> Reporter: Alex Herbert
> Assignee: Alex Herbert
> Priority: Minor
> Fix For: 1.4
>
>
> The Trigamma function increments the input argument by 1 until it exceeds the
> threshold of 49. This is not suitable for large negative values (below -2^53)
> as the increment does not increment the argument.
> Note that double values above 2^53 in magnitude are integers. For negative
> arguments any integer is a pole of the trigamma function and has the value
> +infinity.
> However smaller magnitude arguments may take prohibitively long to compute by
> incrementing. In this case it is possible to use the reflection formula:
> {noformat}
> trigamma(x) + trigamma(1 - x) = pi^2 / sin^2(pi * x)
> if x < 0:
> trigamma(x) = pi^2 / sin^2(pi * x) - trigamma(1 - x){noformat}
> Issue identified using a security scan.
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