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Re: Threads in IDL 7.0 [message #63087]

Tue, 28 October 2008 08:45

Allan Whiteford
Messages: 117
Registered: June 2006

Senior Member

Vince Hradil wrote:
> On Oct 27, 12:26 pm, Heinz Stege <public.215....@arcor.de> wrote:
>
>> On Mon, 27 Oct 2008 16:44:29 +0100, Bernhard Reinhardt wrote:
>>
>>> Well, I wasnï¿½t really precise. Iï¿½m not doing this on a 1d-array but on a
>>> 4d-array, where 2 dimensions are time and 2 dimensions are space. I try
>>> to filter special events in time and count those on a 2d-map. Hereï¿½s the
>>> code:
>>
>>> for i = 0, N_ELEMENTS(STRUC.data[*,0,0,0])-1 do begin
>>> for j = 0, N_ELEMENTS(STRUC.data[0,*,0,0])-1 do begin
>>> indices = Where(STRUC.data[i,j,*,*] GE 150., count)
>>> freq [i,j]=count
>>> endfor
>>> endfor
>>
>>> Although the array data is quite big "where" only getï¿½s a small portion
>>> to see of it. So thread-pool isnï¿½t invoked. => CPU-Usage still 50%
>>
>>> I also asked some more IDL-experienced colleagues about generating
>>> threads manually but they also didnï¿½t know about anything like that :(
>>
>>> BUT using your method still brought me a gain of 3.6 times faster
>>> execution :)
>>
>>> regards
>>
>>> Bernhard
>>
>> Please try the following command:
>>
>> freq=total(total(STRUC.data ge 150.,4,/integer),3,/integer)
>>
>> The IDL manual says, that TOTAL makes use of IDLï¿½s thread pool. And
>> there is no for-loop needed anymore...
>>
>> HTH, Heinz
>
>
> At the risk of repeating myself (I tried to post this earlier, but it
> hasn't shown up?):
>
> Which is faster - (1)TRANSPOSE and TOTAL over leading dims or (2)
> TOTAL over trailing dims
>
> Here's my quick (un-scientific) test:
>
> IDL> arr = bytscl(randomu(sd, [100,101,102,103]))
> IDL> t0 = systime(1) & help, total(total(arr,4,/integer),3,/integer) &
> print, systime(1)-t0
> <Expression> LONG64 = Array[100, 101]
> 0.42199993
> IDL> t0 = systime(1) & help, total(total(transpose(arr,[2,3,0,1]),1,/
> integer),1,/integer) & print, systime(1)-t0
> <Expression> LONG64 = Array[100, 101]
> 1.7979999
> IDL> print, !version
> { x86 Win32 Windows Microsoft Windows 7.0 Oct 25 2007 32 64}

It makes a certain amount of sense that doing the total over trailing
dims would be faster. When you take the transpose IDL is having to go
over the array in a non-optimal fashion anyway so you'd be as well
extracting the totals at the same time.

The solution given by Heinz goes over the data in a non-optimal way (a)
getting the totals (b).

The solution given by me goes over the data in a non-optimal way (1),
copying all the data (2) then goes over the copied data in an optimal
way (3) getting the totals (4).

In the above (a) and (1) will take about the same time as will (4) and
(b). So I'm doing (2) and (3) which Heinz wasn't. I'd expect (3) to be
fairly quick but I guess (2) will be the one which eats up the
unnecessary time.

In my defense I only looked at the loops from Lajos' solution and seen
than they could go - I didn't step back and look at the original
question to see a better overall solution.

I never knew (or forgot about) the /integer keyword to total().

Thanks,

Allan

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[Message index]

		Re: Threads in IDL 7.0 By: Allan Whiteford on Tue, 28 October 2008 08:45
		Re: Threads in IDL 7.0 By: Vince Hradil on Tue, 28 October 2008 07:31
		Re: Threads in IDL 7.0 By: Vince Hradil on Tue, 28 October 2008 06:01
		Re: Threads in IDL 7.0 By: Bernhard Reinhardt on Tue, 28 October 2008 01:28
		Re: Threads in IDL 7.0 By: David Fanning on Mon, 27 October 2008 11:07
		Re: Threads in IDL 7.0 By: Allan Whiteford on Mon, 27 October 2008 10:27
		Re: Threads in IDL 7.0 By: Heinz Stege on Mon, 27 October 2008 10:26
		Re: Threads in IDL 7.0 By: Allan Whiteford on Mon, 27 October 2008 10:23
		Re: Threads in IDL 7.0 By: Foldy Lajos on Mon, 27 October 2008 09:59
		Re: Threads in IDL 7.0 By: Allan Whiteford on Mon, 27 October 2008 09:46
		Re: Threads in IDL 7.0 By: Foldy Lajos on Mon, 27 October 2008 09:11
		Re: Threads in IDL 7.0 By: Bernhard Reinhardt on Mon, 27 October 2008 08:44
		Re: Threads in IDL 7.0 By: David Fanning on Mon, 27 October 2008 06:23

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