From maintainers-request at octave dot org Sun Jan 30 00:49:46 2005
Subject: Re: min function very slow?
From: "Dmitri A. Sergatskov" <dmitri at unm dot edu>
To: Daniel J Sebald <daniel dot sebald at ieee dot org>
CC: maintainers at octave dot org
Date: Sat, 29 Jan 2005 23:51:41 -0700

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Daniel J Sebald wrote:
> Dmitri A. Sergatskov wrote:
> 
>> Daniel J Sebald wrote:
>>
>>>
>>>
>>> Thank you... so do you think your increase for mintime is a blip in 
>>> the OS?  Yours is a factor of 4.5 difference, mine is a factor of 76.
>>>
>>
>> I do not understand this at all. More over on my other computer 
>> (AthlonXP 1666 MHz)
>> the mintime is 2 seconds... The same OS etc...
> 
> 
> 
> So I'm not dreaming.  :-)
> 
> I put a script in my path to redefine min(x) as -max(-x).  That gets me 
> down to the numbers your quoting.  I'll see if I can run a profiler on 
> this.  I don't think it is in dNDArray.cc where it is spending its time.
> 

I rewrote your script as a function (attached). Here is some numbers:

octave:1> [loopt,mint,maxt]=mmt(10000)
loopt = 0.040803
mint = 0.19301
maxt = 0.22110
octave:2> [loopt,mint,maxt]=mmt(10000)
loopt = 0.031585
mint = 0.18326
maxt = 23.859
octave:3> [loopt,mint,maxt]=mmt(10000)
loopt = 0.039405
mint = 0.18089
maxt = 22.695

On SMP computer (octave compiled with -lpthread, otherwise the same flags):

octave:1> [loopt,mint,maxt]=mmt(10000)
loopt = 0.033668
mint = 0.15524
maxt = 0.18152
octave:2> [loopt,mint,maxt]=mmt(10000)
loopt = 0.026402
mint = 0.14753
maxt = 2.6565

As you can see the first time it runs it gets reasonable numbers, after that it goes nuts.

> Dan
> 

Dmitri.

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function [looptime,maxtime,mintime]=mmt(N_loop)
tic();
for i=1:N_loop
  j = i;
end
looptime = toc();
for i=1:N_loop
  j = max(i);
end
maxtime = toc() - looptime;
for i=1:N_loop
  j = min(i);
end
mintime = toc() - maxtime;
endfunction


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