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Re: find max in 3D array -- slow [message #70374 is a reply to message #70370]

Sun, 11 April 2010 04:04

Maxwell Peck
Messages: 61
Registered: February 2010

Member

On Apr 11, 8:44 pm, Maxwell Peck <maxjp...@gmail.com> wrote:
> On Apr 11, 2:03 am, "Timothy W. Hilton" <hil...@meteo.psu.edu> wrote:
>
>
>
>> Hello IDL users,
>
>> I have a 1200x1200x2900 array of floats. The dimensions correspond to
>> latitude x longitude x time. I need to find the maxium at each
>> location -- that is, I need the 1200x1200 array containing the max
>> along the 3rd dimsion. IDL takes almost 3 minutes to do this on my
>> system. This seemed slow. I compared it with Matlab, which took ten
>> seconds. Is there a better way to search for the maxima using IDL?
>
>> The demo code I used to compare IDL and Matlab is below (with output).
>
>> I'm wondering if I ought to switch to Matlab. I just spent a couple
>> of days writing IDL code to read my data, so I'd rather not.
>
>> Many thanks,
>> Tim
>
>> --
>
>> Timothy W. Hilton
>> PhD Candidate, Department of Meteorology
>> The Pennsylvania State University
>> 503 Walker Building, University Park, PA 16802
>> hil...@meteo.psu.edu
>
>> ========
>> scratch.pro:
>
>> foo = randomu(0, 1200, 1200, 2920)
>> PRINT, systime()
>> foo_max = max(foo, DIMENSION = 3)
>> PRINT, systime()
>> END
>
>> IDL> .run scratch
>> % Compiled module: $MAIN$.
>> Sat Apr 10 10:44:44 2010
>> Sat Apr 10 10:47:36 2010
>> IDL>
>
>> ========
>> scratch.m:
>
>> foo = rand(1200,1200,2920);
>> fprintf('%s\n', datestr(now()));
>> foo_max = max(foo, [], 3);
>> fprintf('%s\n', datestr(now()));
>
>>>> scratch
>
>> 10-Apr-2010 10:42:45
>> 10-Apr-2010 10:42:55
>
> I don't know if it's any quicker, and it will sure chew some memory
> but sort_nd might be worth a try.
>
> http://www.dfanning.com/programs/sort_nd.pro
>
> Just sort it along the 3rd dimension and then pull the slice of the
> last band...

I think sort_nd is going to be much slower on testing. Max in IDL does
seem to be a lot slower than what i'd expect in IDL.

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[Message index]

		Re: find max in 3D array -- slow By: Maxwell Peck on Sun, 11 April 2010 14:41
		Re: find max in 3D array -- slow By: Foldy Lajos on Sat, 10 April 2010 11:23
		Re: find max in 3D array -- slow By: Gray on Sun, 11 April 2010 05:37
		Re: find max in 3D array -- slow By: Gray on Sun, 11 April 2010 05:29
		Re: find max in 3D array -- slow By: Maxwell Peck on Sun, 11 April 2010 04:04
		Re: find max in 3D array -- slow By: Maxwell Peck on Sun, 11 April 2010 03:44
		Re: find max in 3D array -- slow By: Mort Canty on Sat, 10 April 2010 11:48
		Re: find max in 3D array -- slow By: Maxwell Peck on Mon, 12 April 2010 01:07

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