Re: Division still cost more than multiplication?
- To: mathgroup at smc.vnet.net
- Subject: [mg24290] Re: Division still cost more than multiplication?
- From: Harald Giese <giese at ifm.uni-hamburg.de>
- Date: Fri, 7 Jul 2000 00:11:31 -0400 (EDT)
- Organization: Institut fuer Meereskunde, Universitaet Hamburg
- References: <8k0tc4$q2o@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
AES wrote:
>
> Old-time FORTRAN programmers (like me) were taught (at least in early
> days) that division cost a lot more machine cycles than multiplication.
> So, if you had an expression like y = x/c that was going to be called
> many times inside a loop, where x and y were variables and c a constant,
> you'd code this as:
>
> (Outside the loop)
>
> cInverse = 1/c;
>
> (Begin loop structure)
>
> y = cInverse * x
>
> Does this still make any sense in Mathematica? Or is it a primitive
> relic of long-gone days?
Hi,
Just check it:
c = 7.7; cInv = 1./c;
Timing[Do[y = x/c, {x, 0, 10000}]]
{0.631 Second, Null}
Timing[Do[y = x*cInv, {x, 0, 10000}]]
{0.34 Second, Null}
/Harald
--
Harald Giese
Email: giese at dkrz.de
Phone: +49 (0)40 42838 5796; Fax: +49 (0)40 5605724
Institut fuer Meereskunde der Universitaet Hamburg
(Institute of Oceanography of the University of Hamburg)
Troplowitzstrasse 7, D-22529 Hamburg