[Scipy-tickets] [SciPy] #849: Cephes Bessel I overflows unnecessarily early

SciPy scipy-tickets@scipy....
Sat Jan 17 13:53:50 CST 2009


#849: Cephes Bessel I overflows unnecessarily early
---------------------------+------------------------------------------------
 Reporter:  pv             |       Owner:  somebody 
     Type:  defect         |      Status:  new      
 Priority:  normal         |   Milestone:  0.8.0    
Component:  scipy.special  |     Version:  devel    
 Severity:  minor          |    Keywords:  bessel iv
---------------------------+------------------------------------------------
 Cephes's implementation of iv overflows to inf early, as results in
 intermediate steps (hyperg, mainly) overflow:
 {{{
 >>> import scipy.special as sc
 >>> sc.iv(0, 356)
 8.59356428766e+152
 >>> sc.iv(0, 357)
 inf
 }}}
 Specfun's implementation doesn't overflow like this:
 {{{
 >>> sc.iv(0, 356+0j)
 (8.5935642876615831e+152+0j)
 >>> sc.iv(0, 357+0j)
 (2.3326966986010146e+153+0j)
 }}}

 There are many ways to fix this, eg. switching to use an asymptotic
 expansion for Iv directly in the correct regime (this needs writing the
 code for this).

-- 
Ticket URL: <http://scipy.org/scipy/scipy/ticket/849>
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