Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!hc!lanl!jlg
From: jlg@lanl.gov (Jim Giles)
Newsgroups: comp.lang.fortran
Subject: Re: intrinsic functions, math operators (was: i++, i+=1, i=i+1)
Message-ID: <4032@lanl.gov>
Date: 22 Sep 88 19:00:46 GMT
References: <1033@amelia.nas.nasa.gov>
Organization: Los Alamos National Laboratory
Lines: 21

From article <1033@amelia.nas.nasa.gov>, by fouts@lemming.nas.nasa.gov.nas.nasa.gov (Marty Fouts):
> This is true, but only accurate when the expression evaluates to a
> constant.  You couldn't (because of finite precision) replace
> 1-COS(X)*COS(X) with SIN(x)*SIN(x) and guarentee the same results.

True, but Fortran would allow this anyway since optimized expressions
need only to be mathematically identical, not computationally identical
(see section 6.6 of the standard).
 
> that you are contemplating to Macsyma, Mathematic, et al.
                                                  ^

That's Mathematica.  And I agree.  I have long wanted to write the
mathematics preprocessor that Knuth talks about.  In fact, I want a
more powerful system which could take (for example) a set of differential
equations and a 3-d initial geometrical set-up and automatically
generate a Fortran code which efficiently runs a finite differencing
technique on the problem.

J. Giles
Los Alamos