From Jerry.Lewis at biogenidec.com  Thu Feb 26 16:15:11 2009
From: Jerry.Lewis at biogenidec.com (Jerry.Lewis at biogenidec.com)
Date: Thu, 26 Feb 2009 16:15:11 +0100 (CET)
Subject: [Rd] besselI inaccurate for negative integer order (PR#13556)
Message-ID: <20090226151511.C1D272834311@mail.pubhealth.ku.dk>

Full_Name: Jerry W. Lewis
Version: 2.8.1
OS: Windows XP Professional
Submission from: (NULL) (198.180.131.16)


It should be the case that
  besselI(x,-nu) == besselI(x,nu) == besselI(x,abs(nu))
for integer nu, yet R currently can return ridiculous values when nu is a
negative integer.

For instance, besselI(9.6,-44) returns -234626490 instead of the correct value
of 5.9041042646307223e-25, while besselI(9.6,44) gives essentially machine
accuracy.

This is more than an idle mathematical curiosity, since one consequence is that
dskellam in the VGAM package can return values <0 or >1.



[Rd] besselI inaccurate for negative integer order (PR#13556)
Jerry.Lewis at biogenidec.com