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MathGroup Archive 2000

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Re: Division still cost more than multiplication?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24303] Re: Division still cost more than multiplication?
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 7 Jul 2000 00:11:45 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <8k0tc4$q2o@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

Timing[x = 1; c = N[\[Pi]]; cInverse = 1/c; Do[y = x*cInverse, {10000}]]
{0.26 Second, Null}

Timing[x = 1; c = N[\[Pi]]; cInverse = 1/c; Do[y = x/c, {10000}]]
{0.41 Second, Null}

The multipication/division algorithm has not changed since several
hundred years -- what are long-gone days for you ? 

You can stopp the time by hand *you* need to multiply two
numbers and to divde the numbers.

Regards
  Jens

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?


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