[Scipy-tickets] [SciPy] #503: bug in special function iv for large argumen

SciPy scipy-tickets@scipy....
Fri Sep 21 05:56:22 CDT 2007


#503: bug in special function iv for large argumen
----------------------+-----------------------------------------------------
 Reporter:  mbakker7  |       Owner:  somebody
     Type:  defect    |      Status:  new     
 Priority:  normal    |   Milestone:  0.7     
Component:  Other     |     Version:          
 Severity:  normal    |    Keywords:          
----------------------+-----------------------------------------------------
 The modified Bessel function iv returns incorrect values for large
 argument.

 iv(0,100) gives 5.72185663838e+041

 while the equivalent is

 jv(0,complex(0,100))
 (1.07375170713e+042+0j )

 This latter results is the correct answer, as verified in Abramowitz and
 Stegun, Table 9.11, Page 428. Using the jv is a work-around, but this
 should probably be fixed. The two results start to deviate for arguments
 over about 50, with jv giving the correct answer. The same goes wrong for
 iv of other integer order (I did not check non-integer orders).

 On a related note, there are implementations for Bessel functions of
 integer order (jn, kn) but not for the modified Bessel function In. I
 guess this is because the function would be called 'in', but it would be
 nice to have a special function for integer order, and I am pretty sure
 they are around.

 Thanks, Mark

-- 
Ticket URL: <http://scipy.org/scipy/scipy/ticket/503>
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