Path: utzoo!utgpu!water!watmath!clyde!rutgers!cmcl2!beta!jss
From: jss@beta.UUCP (Jeffrey Saltzman)
Newsgroups: comp.lang.fortran
Subject: Re: Want Fast Double Precision?
Message-ID: <15008@beta.UUCP>
Date: 29 Jan 88 16:36:58 GMT
References: <32300003@ccvaxa>
Organization: Los Alamos Natl Lab, Los Alamos, N.M.
Lines: 39

in article <32300003@ccvaxa>, aglew@ccvaxa.UUCP says:
> Nf-ID: #N:ccvaxa:32300003:000:1342
> Nf-From: ccvaxa.UUCP!aglew    Jan 21 10:15:00 1988
> 
> 
> /* Written 10:14 am  Jan 21, 1988 by aglew@ccvaxa.UUCP in ccvaxa:comp.arch */
>>	I really don't think the real world really needs anything more
>>expansive than a 32 bit processor to get most jobs done.
> 
> Probably, but... I wonder how much interest might be out there for
> a true double-precision floating point engine - one that did 64 bit
> floating point, or IEEE 80 bit extended floating point, or even 
> 128 bit floating point, as its native floating point mode, as fast
> as single precision on nearly any other machine in its price range?
> 
The Cray series of machines are 64 bit machines.  That is single
precision on these machines is 64 bits.  The reason for going this
route was rounding errors on large programs were beginning to
cause large perturbations in problems.  One example of why this
should happen is with linear systems derived from finite difference
methods for partial differential equations.  Although the algorithms
derived are stable the condition numbers of the matrices increase
with the size of the problem solved.  The amount of rounding error
is related to the condition number of the matrix.  See Forsythe and
Moler, "Computer Solution of Linear Algebraic Systems" (Prentice-Hall).

> I'm sure that most people wouldn't need this, but some might - and I'd 
> like to get a feel for the size of such a niche, if it exists. 
> 
With the increased availablity of fast CPUs more and more people might
be inclined to require more bits for their calculations since they might
want to do larger problems.

---------------------
Jeff Saltzman
Los Alamos National Laboratory
jss@lanl.gov

disclaimer:remialcsid