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Re: Threads in IDL 7.0 [message #63109 is a reply to message #63108]

Mon, 27 October 2008 10:23

Allan Whiteford
Messages: 117
Registered: June 2006

Senior Member

Fďż˝LDY Lajos wrote:
>
> On Mon, 27 Oct 2008, Bernhard Reinhardt wrote:
>
>> David Fanning wrote:
>>
>>> Bernhard Reinhardt writes:
>>>
>>>> I have have read the Chapter "Multithreading in IDL" in the
>>> IDL-Help. As > far as I can see some IDL functions use threads.
>>>> > Basically I want to count elements of a big array that exceed a
>>> given > number.
>>>> > count=0
>>>> for i = 0, 200000 do begin
>>>> if array[i] ge 10. then count++
>>>> endfor
>>>
>>> How about something like this:
>>>
>>> indices = Where(array GE 10, count)
>>
>>
>> Well, I wasnďż˝t really precise. Iďż˝m 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.
>> Hereďż˝s 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)
>
>
> You are accessing elements in the wrong order, resulting in cache misses
> if struc.data is greater than the CPU data cache.
>
>> freq [i,j]=count
>> endfor
>> endfor
>>
>
> Try this:
>
> d=transpose(struc.data, [2,3,0,1])
> dims=size(d, /dim)
> for i = 0, dims[2]-1 do begin
> for j = 0, dims[3]-1 do begin
> indices = Where(d[*,*,i,j] GE 150., count)
> freq [i,j]=count
> endfor
> endfor
>
>
> regards,
> lajos

Or this:

freq = fix(total(total(transpose(struc.data,[2,3,0,1]) ge 150.,1),1))

which should go faster because of the lack of loops.

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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