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find max in 3D array -- slow [message #70378]

Sat, 10 April 2010 09:03

Timothy W. Hilton
Messages: 1
Registered: April 2010

Junior Member

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
hilton@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

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[Message index]

		find max in 3D array -- slow By: Timothy W. Hilton on Sat, 10 April 2010 09:03
		Re: find max in 3D array -- slow By: JDS on Mon, 12 April 2010 10:48
		Re: find max in 3D array -- slow By: Juggernaut on Mon, 12 April 2010 09:20
		Re: find max in 3D array -- slow By: Steve[5] on Mon, 12 April 2010 04:15
		Re: find max in 3D array -- slow By: Maxwell Peck on Mon, 12 April 2010 03:36

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