Re: Fortran better than Lisp for numerical code?

[tjj@ssc-vax.UUCP (T J Jardine)]

> There has been much discussion of late about comparing Lisp and Fortran
> for numerical code.  Many people have either stated or implied that
> Fortran should be better for number crunching than Lisp.  Why do people
> believe that?  Why should a Fortran compiler produce any better code for
> 	A=B*C
> than a Lisp compiler would produce for
> 	(setq a (* B C))
> (assuming, in the latter case, appropriate declarations or use of
> non-generic functions)? ...

I won't try to speak about what others mean,  but I know that what I mean when
I say that Fortran is  "better"  for numeric computations has nothing to do at
all with  a=b*c  or its ilk.   Certainly  with appropriate attention to detail
Lisp can handle  (setq a (* b c))  with just as much efficiency.   Fortran (or
Pascal, ...)  is a more appropriate choice  if the numeric computations are at
a higher level,  such as  the computations  involved in  simulating the flight
dynamics of an air vehicle,  or in solving celestial navigation problems.   In
such a case  the optimum  is that  the problem solution already exists and one
must  "link"  to  the  solution  and  obtain  its results.  In a slightly less
optimal situation  a library of subroutines/functions  exists which need to be
coupled  in some  obvious  way  and  then  this  coupling "linked" to the Lisp
environment to obtain the solution.

The point is,  I believe, that just because we have Lisp, or a new "AI problem
solving approach"  does not mean that we should reinvent all problem solutions
using  this new approach.   Decision tables still provide an effective problem
solving tool for certain classes of problems  -- why not use such a capability
when it is applicable?   It may be the case  that other factors will influence
us to rewrite a solution using our new tool or approach -- I hope I don't ever
have  to write another  communications control program in COBOL,  for example,
although  COBOL  was indeed  capable of handling the particular problem at the
time.   By the way,  double precision  floating point  is the default in Franz
Lisp  (I haven't  yet found  a way to create a single precision variable,  but
haven't pursued it that far), and I know double precision is also available in
Zetalisp.   The  list  very  likely  larger than just those two -- Common Lisp
probably has it.

Ted Jardine
TJ (with Amazing Grace) The Piper
Boeing Artificial Intelligence Center
...uw-beaver!ssc-vax!bcsaic!ted
-- 
TJ (with Amazing Grace) The Piper
Boeing Artificial Intelligence Center
...uw-beaver!ssc-vax!bcsaic!ted