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MathGroup Archive 1994

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Re: PowerPCs

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Re: PowerPCs
  • From: Richard Mercer <richard at rmercer.wright.edu>
  • Date: Fri, 01 Jul 1994 14:25:48 -0700

To: Dave Withoff

Thanks for your knowledgable and informative review of timing methods.

I was primarily concerned with two things:
(1) People unintentionally comparing "Timing" results with "front end" results  
because they were unaware of what the other person was doing.
(2) I know that the front end timing on a certain NeXT workstation is  
systematically off by about 20%. I don't know that this problem does not arise  
on other platforms. That's why I asked people to CHECK timings with a
stopwatch, NOT RELY on stopwatch timings.

    An example of what I am trying to avoid is on p.5 of the 5.30.94 MacWeek,  
where a "Timing" result of ListPlot is given as 4.48 seconds on a PowerMac,  
which does not include the considerable time for rendering the Postscript  
graphic. This is claimed to take 27.3 seconds on a Quadra 700, a result which  
almost certainly is total elapsed time. In fact this same calculation on the  
aforementioned NeXT, which uses the same processor as the Quadra 700 (25mhz  
68040), takes 28 seconds elapsed time but gives a Timing result of 8.4 seconds.  
(The front end shows 34 seconds!)
    The result is that WRI, in a national publication, seems to be claiming (I  
assume unintentionally) that Mathematica on the PowerMac is 6 times as fast as  
on a Quadra 700; the truth seems to be that it is roughly twice as fast on this  
particular calculation. While the comparison shown may serve the short-term  
interests of Apple Computer and/or WRI, in the long run we'll all be better off  
with the more more realistic comparison.
   (Incidentally, I have recently bought a PowerMac 7100, am very pleased with  
it, and think the combination of this machine with the Macintosh front end is  
the best or close to the best Mathematica platform currently available. If I  
didn't think Mathematica was a great program, I wouldn't be on this list!) 


Personally, I think "Timing" results are much less useful for users than for  
systems engineers. Users likely want to know how long something actually takes,  
and are less interested in why.

*********************************************************************
Richard Mercer                             513-873-2191 office
Department of Mathematics and Statistics   513-873-2785 message
Wright State University                    513-429-2179 fax
Dayton, OH 45435                           NeXTmail welcome!
richard at rmercer.wright.edu        or       rmercer at desire.wright.edu
*********************************************************************





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