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[math] Proposal: logsumexp

Hello friends, I'm new to Java, and to Apache Commons Math, and I'm porting some code to Java. One useful function that's available in Scipy is `logsumexp`:


In a nutshell, given a list of values in the log domain, the function numerically-stably sums them, yielding the result still in the log domain.

This is useful for me because I need to add and subtract the results of the log-Gamma function (via your `Gamma.logGamma`). For *subtraction,* Scipy's `logsumexp` can accept a *second* list giving the scalars to apply to each value (e.g., +1, -1), and returns both the magnitude *and* sign of the result.

I would like feedback on adding `logsumexp` to Apache Commons Math. I have ported the Python version, from


to Java, which lives at:


As mentioned above, I'm a beginner, and am experimenting with Java 8 Collections, etc., so I am embarrassed by my mixing of `List` and plain arrays in this last link above. Assuming that you think it would be a good addition to Math, I'm totally open to suggestions to improve the API.

Many thanks,


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