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Re: Non-deterministic numerical inaccuracies in

  • To: mathgroup at smc.vnet.net
  • Subject: [mg95773] Re: Non-deterministic numerical inaccuracies in
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Tue, 27 Jan 2009 06:56:37 -0500 (EST)
  • References: <gjcuio$cnf$1@smc.vnet.net> <gjkvd4$92g$1@smc.vnet.net> <glj89b$dj0$1@smc.vnet.net>

danl at wolfram.com wrote:
>> Daniel Lichtblau wrote:

> 
> My understranding is that the library vendors do not regard it as broken,
> so I am not optimistic that the library itself will change. We have made
> some effort to align machine floats to 16 bits so this particular behavior
> should stabilize in a future release.
> 
> I am not really competent to discuss the issues involved in going to a
> different library. Maybe others can address that. I can only voice my
> suspicion that it would be difficult, and offer dubious gain.
> 
> 
Surely aligning floats on 16-bytes would only be a partial fix because 
if an array A were packed and 16-bytes aligned, A[2;;] would only be 
8-bytes aligned!

It seems to me that it was a wretched decision of the C compiler writers 
to plant code that delivers different results - however insignificant - 
depending on data alignment! I wonder if anyone has reported to them 
that this difference exists!

I was not suggesting using a different library - only a previous version 
- such as that used inside 6.0.3, which was presumably compiled with an 
earlier compiler.

The mere fact that several people have discovered this problem, suggests 
to me that it will be an irritant.

David Bailey
http://www.dbaileyconsultancy.co.uk


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