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07 May 2014 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Maarten

Hi Darren,

Great script you have here. Do you have any ideas where i can find some more information about the differentiation algorithm you are using?

thanks

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07 May 2014 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Maarten

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20 Mar 2014 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Philip Ohnewein

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29 Jan 2014 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Philip Ohnewein

Tested it for 1-dimensional data only: Easy to use, does exactly what it is expected to do. Thank you very much!

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18 Dec 2013 ONEPERM Obtain a single permutation of the numbers 1:N Author: Darren Rowland Peter Li

Peter Li (view profile)

Ah, based on recursive permutation as here: http://www.mathworks.com/matlabcentral/fileexchange/13060-perms1

So not in the same order as Matlab PERMS or C++ STL NEXT_PERMUTATION. I guess this means I can't use this as starting points for a multithreaded version based on STL.

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30 Jan 2013 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Nek Valous

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04 Mar 2012 ONECOMB Obtain a single combination of N numbers taken K at a time. Author: Darren Rowland Alexey

Alexey (view profile)

Very useful!

What's about reverse function converting conbination to its index?

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18 Nov 2010 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Darren Rowland

@ Carlos,
Yes this will handle equally spaced data too. The formula I have used reduces to the central difference formula when the data are equally spaced, so the result is mostly the same as GRADIENT in that case.
The first example in the file demo_diffxy demonstrates the case of equally spaced points (follow the link next to 'Published MATLAB Files' above to view).
Darren

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16 Nov 2010 diffxy Second-order accurate numerical differentiation (N-dimensional) Author: Darren Rowland Carlos

Carlos (view profile)

I noticed that you specified that this file was made to handle unequally spaced data but, I was wondering if it can also handle equally spaced data? Thank you.

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24 Mar 2010 ONECOMB Obtain a single combination of N numbers taken K at a time. Author: Darren Rowland Husam Aldahiyat

Very useful submission, well written.

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16 Jan 2010 ONECOMB Obtain a single combination of N numbers taken K at a time. Author: Darren Rowland Rob Campbell

Rob Campbell (view profile)

This well coded and does what it says. Can be substantially faster than nchoosek. For example:

>> tic, for i=1:1E4;onecomb(10,5,5);end,toc/1E4
ans =
7.3127e-05
>> tic, for i=1:1E4;NCHOOSEK(1:10,5);end,toc/1E4
ans =
3.7945e-04

The 1 star review seems to have missed the point.

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15 Dec 2009 ONECOMB Obtain a single combination of N numbers taken K at a time. Author: Darren Rowland Darren Rowland

@ Marco/PXlab

It is exactly correct that this function with call structure

C1 = onecomb(N,K,M)

returns the same result as

AC = nchoosek(N,K);
C2 = AC(M,:)

The advantage of this function is that the intermediate array AC is not computed by ONECOMB. The array AC can be immensely large for large N and K approx N/2, and is a waste to compute if one only requires a small number of combinations from the total.

Additionally, if one requires many combinations, my testing (not included here but simple to duplicate) showed that the time to compute all the combinations using NCHOOSEK was approximately the same as computing all the combinations one-at-a-time using ONECOMB.

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28 Apr 2009 FACTORADIC Obtain the factorial radix representation of a number. Author: Darren Rowland John D'Errico

John D'Errico (view profile)

A useful tool when generating permutations. In fact, I was thinking of putting up this myself. No need to do so now.

Good help. Error checks. Simple engine.

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