From maintainers-request at octave dot org Sun Jan 30 01:07:33 2005
Subject: Re: min function very slow?
From: Daniel J Sebald <daniel dot sebald at ieee dot org>
To: "Dmitri A. Sergatskov" <dmitri at unm dot edu>
Cc: maintainers at octave dot org
Date: Sun, 30 Jan 2005 01:13:46 -0600

Dmitri A. Sergatskov wrote:

> 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.


Sure 'nough.  (You've switched maxt and mint, but point taken.)  Look at 
what I'm getting:

octave:1> [loopt, maxt, mint] = mmt(10000)
loopt = 0.10684
maxt = 0.50235
mint = 0.51636
octave:2> [loopt, maxt, mint] = mmt(10000)
loopt = 0.087893
maxt = 0.47367
mint = 71.194

Everything in the code looks so symmetric with regard to min and max.  
Strange.

Could a header file definition of "min" be substituting code that 
somehow still compiles?  (Wild, wild guess.)

Dan