array precision

[Barry Drake]

Michael,
Sorry you missed my point.  Try "Intro to Matrix Computations" by
Stewart, first few chapters for the numerical portion.  As for the
double versus float, that is what I read in Beasley's book, which I
mentioned.  I'm new to Python and obviously don't have the vast
experience you have.  But, I'll keep trying.

Regards,
Barry Drake

Michael Hudson <mwh at python.net> wrote in message news:<ug04da4k1.fsf at python.net>...
> bldrake1 at yahoo.com (Barry Drake) writes:
> 
> > Maybe I'm missing something, but here is what I get:
> 
> Well, I'm missing your point.
> 
> > Python 2.1.1 (#20, Jul 26 2001, 11:38:51) [MSC 32 bit (Intel)] on
> > win32
> > Type "copyright", "credits" or "license" for more information.
> > IDLE 0.8 -- press F1 for help
> > >>> import math
> > >>> n = 10
> > >>> nf = 10.0
> > >>> a = 1.0
> > >>> b = 0.5
> > >>> a/n
>  0.10000000000000001
> > >>> b + a/n
>  0.59999999999999998
> > >>> a/nf
>  0.10000000000000001
> > >>> b + a/nf
>  0.59999999999999998
> > >>> 
> > 
> > Python does double precision floats only (see Python Essential
> > Reference 2nd ed. by David Beazley, p.23).
> 
> But you can have arrays (as in, objects of type array.ArrayType) that
> store C single floats.  Which was Jason's point.
> 
> > Python implements IEEE 754: 17 digits of precision with exponent in
> > -308 to 308.
> 
> Oh No It Doesn't.  Python uses (for the objects of type
> types.FloatType) whatever the C compiler that compiled it called
> "double".  This may be IEEE 754 doubles on the platforms you've used,
> but there's certainly no guarantee of that (e.g. Crays, IBM boxes (I
> think)).
> 
> >          float     double
> > python   64 bits   64 bits
> > C        32 bits   64 bits
> 
> "python double" is meaningless.
> 
> > BTW, you might want to check out the Numeric module in the NumPy
> > distribution at http://numpy.sourceforge.net.
> 
> That lets you store floats or doubles too.
> 
> Cheers,
> M.