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From Brian Wignall <brianwign...@gmail.com>
Subject [math] Bessel functions
Date Mon, 25 Nov 2013 13:46:46 GMT
Hello, everyone.

I am new and hoping to make my first contribution. I read through the Wish
List, and I thought I could help quickly by starting with the special
functions request.

I created a JIRA (https://issues.apache.org/jira/browse/MATH-1066) that
contains a patch for Bessel functions of the first kind. There are other
Bessel functions that are relevant, but I figured I would post that, to get
(minor, hopefully) suggestions or tweaks to get it ready, to streamline the
process for other functions.

The JIRA is a bit sparse, so some more details on the patch follow.

Like several other open source packages, I started from Fortran code in
Netlib; in this case, http://www.netlib.org/specfun/rjbesl . As a first
pass, I enabled the double-precision lines with IEEE values already in the
code and then put the Fortran code through f2j (
http://www.netlib.org/java/f2j/). This handled the straightforward parts,
but it left in gotos and some other bits that needed cleaning. Getting the
output of f2j to a decent place took more time and effort than I had
anticipated, but it is passing the unit tests I put in (based on output
from R, which uses a translation of the same Fortran code).

I am looking forward to hearing thoughts and suggestions.

Kind regards,
Brian

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