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https://issues.apache.org/jira/browse/NUMBERS-219?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert updated NUMBERS-219:
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Issue Type: Bug (was: Improvement)
> Digamma and Trigamma limits at -infinity are unspecified; at +infinity are
> defined
> ----------------------------------------------------------------------------------
>
> Key: NUMBERS-219
> URL: https://issues.apache.org/jira/browse/NUMBERS-219
> Project: Commons Numbers
> Issue Type: Bug
> Components: gamma
> Affects Versions: 1.0
> Reporter: Alex Herbert
> Priority: Trivial
>
> The Digamma and Trigamma functions currently return the input argument if it
> is not finite. NaN is returned as NaN and infinity is returned as the same
> infinity. These infinite limits are not correct.
> ||Function||Argument||Limit||Return||
> |Digamma|-infinity|Has infinite poles at integer values.
> As x moves toward negative infinity along the real axis,
> it repeatedly crosses these infinite poles and oscillates between + and -
> infinity.
> The value diverges and has no limit.|NaN|
> |Digamma|infinity|The function grows (logarithmically) without bound to
> infinity|infinity|
> |Trigamma|-infinity|As for the digamma function, the real-valued trigamma
> function
> features infinite poles at all non-positive integers.
> Between these poles it oscillates and does not have a simple limit.|NaN|
> |Trigamma|infinity|The function decays asymptotically like 1 / x towards
> zero.|0|
>
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