[FRPythoneers] Numerical Accuracy

Keith Hellman kehellman at yahoo.com
Sat May 18 17:59:27 MDT 2002


Thanks for the responses...now I remember why I used to have a macro in C:

if( INTERVAL( float_val, float_compare, float_tolerance ))
  // blah
}

See ya monday.

--- Evelyn Mitchell <efm at tummy.com> wrote:
> Python does not support IEEE 754:
>   http://www.amk.ca/python/dev/2000-10-1.html
> 
> There's an open PEP:
>   http://www.python.org/peps/pep-0228.html
> 
> Python supports C and Posix floating point standards.
> 
> Evelyn
> 
> * On 2002-05-18 20:17 Sean Reifschneider <jafo at tummy.com> wrote:
> > On Sat, May 18, 2002 at 01:44:45PM -0600, Evelyn Mitchell wrote:
> > >>>> 29.8
> > >29.800000000000001
> > >
> > >Looks like a bug to me.
> > 
> > Fast floating point approximations sometimes are very bad at dealing
> with
> > certain values.  They go under the assumption that it's ok to be close
> > enough (and to me, 15 digits of precision is close enough for my use).
> > 
> > It's not so much a bug as a trade-off definied by (probably) IEEE fast
> > floating point mechanisms.  The bigger problem is when you find that
> 2.0 +
> > 2.0 != 4.0 -- because of rounding errors and the like...  Which is
> part
> > of the reason I will usually check for "< 1" instead of "== 0"...
> > 
> > Sean
> > -- 
> >  "Who's the guy in the suit?"  "FBI."  "He looks a little to much like
> a
> >  lounge lizard for FBI."  "He's working under-cover."  -- Sean &
> Evelyn 2000
> > Sean Reifschneider, Inimitably Superfluous <jafo at tummy.com>
> > tummy.com - Linux Consulting since 1995. Qmail, KRUD, Firewalls,
> Python
> > _______________________________________________
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> 
> -- 
> Regards,                    tummy.com, ltd 
> Evelyn Mitchell             Linux Consulting since 1995
> efm at tummy.com               Senior System and Network Administrators
>                             http://www.tummy.com/
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=====
Keith E. Hellman
kehellman at yahoo.com

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