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DNorm2

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Fast euclidian norm over N.th dimension of a DOUBLE array

Y = DNorm2(X, N)
INPUT:
X: Real DOUBLE array.
N: Dimension to operate on.
OUTPUT:
Y: Euclidian norm over N.th dimension: Y = sqrt(sum(X .* X, N)).
Length of N.th dimension of Y is 1.
NaN's are considered.

Matlab's built-in function NORM is fast for vectors, but for matrices the matrix norm is replied. Other efficient methods for vectors(!):
Y = sqrt(sum(X .* X));
Y = sqrt(X * X'); % row vectors, faster than DNorm2!
And James Tursa's MTIMESX is very fast for vectors also and can operate on the 1st dimension of arrays also:
X = rand(100, 100); X = reshape(X, 100, 1, 100);
Y = sqrt(mtimesx(X, 't', X));
But for arrays DNorm2 is faster, and I do not see a way to apply MTIMESX for trailing dimensions without time-consuming transpositions.

COMPILATION:
This function must be compiled before using:
mex -O DNorm2.c
See DNorm2.c for detailed instructions.

TEST: Run uTest_DNorm2 to test validity and speed.

NOTES: See DNorm2.c for strategies to optimize processing speed depending on the size of X.
Unfortunately this function is not multi-threaded. Assistence to include OMP would be very welcome.

Tested: Matlab 6.5, 7.7, 7.8, WinXP, 32bit
Compiler: LCC2.4/3.8, BCC5.5, OWC1.8, MSVC2008
Assumed Compatibility: higher Matlab versions, Mac, Linux, 64bit

Free download from Shareware Connection - Fast euclidian norm over N.th dimension of a DOUBLE array

Publisher: Jan Simon | License: Shareware
Version: 1.0 | Size: 10 KB | Platform: Matlab, Scripts
Released Date: 12-03-2013 | Rating: 0 | Title: DNorm2

Author Url: http://www.mathworks.com
Program Info Url: http://www.mathworks.com
Download Url: http://www.mathworks.com/matlabcentral/fx_files/29035/2/DNorm2_16Oct2010.zip

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Shareware Connection periodically updates pricing and software information of 'DNorm2' from company source 'Jan Simon' , so some information may be slightly out-of-date. You should confirm all information before relying on it. Software piracy is theft,  Using 'DNorm2' crack, password, serial numbers, registration codes, key generators is illegal and prevent future development of DNorm2.

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