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MathGroup Archive 1999

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Re: Timing[] and AbsoluteTime[].

  • To: mathgroup at smc.vnet.net
  • Subject: [mg20276] Re: [mg20257] Timing[] and AbsoluteTime[].
  • From: Jean-Marie Thomas <jmt at agat.net>
  • Date: Mon, 11 Oct 1999 02:19:52 -0400
  • Organization: TeA
  • References: <199910100404.AAA09116@smc.vnet.net.>
  • Sender: owner-wri-mathgroup at wolfram.com

Timing returns the CPU time used by the evaluation of your command in the
kernel (and not the kernel plus the frontend)

AbsoluteTime is a date function (number of seconds since January 1,1900)

So, if your command needs 10 sec CPU time, and other processes running on your
computer require 10 more sec, and displaying your results needs 10 sec, Timing
will returns 10, and after minus before 30.

On Sun, 10 Oct 1999, Guilherme Roschke wrote:
> How does timing measure its "value"?
> 
> here is my problem.  I have fuction f[x], which does a few hundred
> NIntegrates.
> 
> Timing[f[x];]
> 
> = {1770.60,Null}.
> 
> However:
> 
> before=AbsoluteTime[];  (# of secs since 1/1/1900)
> 
> Timing[f[x];]
>  = {1770.60,Null}
> 
> after=AbsoluteTime[];
> 
> Diff=after-before
> 
> = 14,673.000
> 
> 
> Timing is off by a factor of 10!
> 
> Note that this is on a DEC with 2 21264 500mhz Alpha chips, where nothing
> else is running except for the system deamons (lpd, sendmail, xserver
> etc...).
> 
> This is especially disconcerting because the AbsoluteTime[] elapsed is
> closer to a PII350 that I have than I would have hoped for in doing
> numerics on the Alpha machine.
> 
> Does anyone have any thoughts of what might be going on?  On how I could
> actually receive my answer in 1,700 rather than 14,000 seconds?
> 
> I'm using version 4 for Digital Unix.
> 
> 
> 
> thanks,
> 
> Guilherme
> 
> *************************************************
> Guilherme Roschke			 	*
> Programmer/SysAdmin/Researcher			*
> Dept. of Anesthesia				*
> University of Pennsylvania Medical School	*
> gr at network3.entropy.upenn.edu			*
> *************************************************


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