[Scipy-tickets] [SciPy] #503: bug in special function iv for large argumen
SciPy
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Fri Sep 21 05:56:22 CDT 2007
#503: bug in special function iv for large argumen
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Reporter: mbakker7 | Owner: somebody
Type: defect | Status: new
Priority: normal | Milestone: 0.7
Component: Other | Version:
Severity: normal | Keywords:
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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
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Ticket URL: <http://scipy.org/scipy/scipy/ticket/503>
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