Re: Division still cost more than multiplication?

*To*: mathgroup at smc.vnet.net*Subject*: [mg24304] Re: Division still cost more than multiplication?*From*: AES <siegman at stanford.edu>*Date*: Fri, 7 Jul 2000 00:11:46 -0400 (EDT)*Organization*: Stanford University*References*: <8k0tc4$q2o@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

In article <8k0tc4$q2o at smc.vnet.net>, AES <siegman at stanford.edu> 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: [snip] > Does this still make any sense in Mathematica? Or is it a primitive > relic of long-gone days? +++++++++++++++++++++++++++++++++++++++++++++ Anticipating replies to my query that I believe are coming from P. J. Hinton and Daniel Lichtbau ((thanks to both), here is the same test as P. J. Hintons, performed on a 1998-model 400 MHz Mac PowerBook G3, giving very similar results: In[7]:= {num, den} = {Random[], Random[]} Out[7]= {0.0991313, 0.0559147} In[8]:= recip = 1.0 / den Out[8]= 17.8844 In[9]:= Timing[Do[num/den, {2000000}]] Out[9]= {28.8 Second, Null} In[10]:= {num, den} = {Random[], Random[]} Out[10]= {0.132828, 0.28853} In[11]:= recip = 1.0 / den Out[11]= 3.46585 In[12]:= Timing[Do[num * recip, {2000000}]] Out[12]= {14.6833 Second, Null}