[SciPy-user] exponential integral behaviour near -20

David Joyner wdj@usna....
Mon Dec 15 23:34:53 CST 2008



---- Original message ----
>Date: Mon, 15 Dec 2008 23:02:30 -0600
>From: "Robert Kern" <robert.kern@gmail.com>  
>Subject: Re: [SciPy-user] exponential integral behaviour near -20  
>To: "SciPy Users List" <scipy-user@scipy.org>
>
>On Mon, Dec 15, 2008 at 22:39, David Joyner <wdj@usna.edu> wrote:
>> Hi:
>>
>> A user reported a bug on the sage-support list (Sage, www.sagemath.org, includes scipy) for the exponential
>> integral. This seems to illustrate the idea:
>>
>>>>> import scipy.special, math
>>>>> -scipy.special.exp1(-complex(19.9999990))
>> (25615628.4058083-3.1415926535897931j)
>>>>> -scipy.special.exp1(-complex(19.9999991))
>> (25615624.582086116+3.1415926535897931j)
>>
>> Any ideas on what would cause this?
>
>I cannot replicate this on OS X with a recent(ish) SVN scipy compiled
>with gfortran 4.2.1. This function is implemented in FORTRAN, so the
>FORTRAN compiler used may be relevant. Can you give us more
>information about the platform, scipy version, and FORTRAN compiler?
>


I think all the version information is here (I ran scipy
from within sage using sage -python):
http://www.sagemath.org/packages/standard/
It was run on a machine with a phenom chip
running amd64 ubuntu 8.10.




>-- 
>Robert Kern
>
>"I have come to believe that the whole world is an enigma, a harmless
>enigma that is made terrible by our own mad attempt to interpret it as
>though it had an underlying truth."
>  -- Umberto Eco
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