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Theophanes Raptis

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NCSR DEMOKRITOS

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Physicist - Scientific Software Developer


 

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06 Aug 2013 Screenshot Computable Complexity Estimates for Finite Binary Strings Experimental attempt to overcome problems with Shannon's entropy and other complexity measures. Author: Theophanes Raptis data exploration, matrix, communications, statistics 7 0
29 Jul 2013 Locating Reducible Words - Free Groups The main function locates all reducible and cyclically reducible words. Author: Theophanes Raptis statistics, combinatorics, groups 6 0
20 Aug 2011 Read - Bajraktarevic Operator Solution of functional equations through an iterative procedure Author: Theophanes Raptis mathematics, modeling 5 0
09 Aug 2011 Screenshot Curl Eigenfields Part-2: The complete Package v1 Both the optimization trick and a new synchronization technique for the 1st order eigen-rotation PDE Author: Theophanes Raptis simulation, mathematics, wireless, communications, physics 6 0
06 Aug 2011 Screenshot Beltrami Problem: Curl Eigen-Fields (WWhW Proj. - Part 1) Solving a 1st Order PDE with an optimization trick. Author: Theophanes Raptis optimization, simulation, wireless, communications, mathematics 5 0
Comments and Ratings by Theophanes Raptis
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28 Jul 2011 Curvilinear Coordinates Programs using curvilinear coordinates, and tensor concepts are given. Author: Howard Wilson

How is one supposed to use the curl function in numeric mode? Tried with
syms r t p cs2 real; names=[r t p];
X=[r*sin(t)*cos(p);r*sin(t)*sin(p);r*cos(t)];% Basis of Covariant Vectors

bcov = [[ cos(t), -r*sin(t), 0], [ sin(t), r*cos(t), 0], [ 0, 0, 1]];


% Christoffel Symbols of the Second Kind

cs2 = zeros(3,3,3);

cs2(:,:,1) = [[ 0, 0, 0], [ 0, -r, 0], [ 0, 0, 0]];

cs2(:,:,2) = [[ 0, 1/r, 0], [ 1/r, 0, 0], [ 0, 0, 0]];

cs2(:,:,3) = [[ 0, 0, 0], [ 0, 0, 0], [ 0, 0, 0]];

curls([1, 2 ,3],names,bcovar,cs2,tn)

and gives

>> curltst
??? The following error occurred converting from sym to double:
Error using ==> sym.double at 25
DOUBLE cannot convert the input expression into a double array.
If the input expression contains a symbolic variable, use the VPA function instead.

Error in ==> curltst at 11
cs2(:,:,1) = [[ 0, 0, 0], [ 0, -r, 0], [ 0, 0, 0]];

Comments and Ratings on Theophanes Raptis' Files View all
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13 Aug 2014 Restricted Integer Composition Generates restricted and unrestricted integer compositions Author: Theophanes Raptis John E.

Tried this out and is pretty slow. Check this out: jdoric(1000,1000,1000,1,1000) - runs forever (didn't even terminate on my PC) although there is just a single integer composition, namely 1000 = 1+1+...+1. Runtime increases exponentially in the number of parts.

10 Aug 2014 Restricted Integer Composition Generates restricted and unrestricted integer compositions Author: Theophanes Raptis Tim Johnson

Tried this-worked out perfectly. Was fast.

10 Mar 2014 Restricted Integer Composition Generates restricted and unrestricted integer compositions Author: Theophanes Raptis iuvaris

Well, it's still my firm view that this algorithm (not the implementation) is awfully slow and no bit more general than other algorithms for restricted integer compositions.

For example, when I set n=16; a=1; b=4; and run

tic; jdoric(n,1,16,a,b); toc

this yields, on my computer, a run time of 21 seconds. Contrarily, when I run

tic; for k=1:16; colex(n,k,a,b); toc

this runs in 2.5 seconds. (Colex is the Vajnovszki/Vernay algorithm that is also available as a matlab implementation).

When I set n=18, run times become 289 seconds and 25.6 seconds, respectively.

So, why on earth would anyone want to use this slow algorithm?

Other issues:
1) The good rating of this algorithm here on mathworks appears to be manipulated.
2) You may wish to google "Corrections" to the Opdyke algorithm "A unified approach ..."

13 Jan 2014 Restricted Integer Composition Generates restricted and unrestricted integer compositions Author: Theophanes Raptis iuvaris

Alright, I agree, John D'Errico, that the argumentation should remain factual.

It's just really difficult to argue with Mr. Opdyke because he apparently doesn't understand some basic principles of the things he has published about. Writing problematic papers is one thing, defending errors beyond reason is another. Whatever his contributions in his paper have been, they have neither been the provision of solutions to open problems nor the provision of a general algorithm for solving the restricted integer composition/partition problem. I think that the "success" of his paper is due to self-promotion - and recipients of his work should be made aware of his paper's and algorithm's deficiencies.

In the interest of his readers, I have summarized my points of critique in a pdf file.
http://www.adiuvaris.org/correction.pdf

12 Jan 2014 Restricted Integer Composition Generates restricted and unrestricted integer compositions Author: Theophanes Raptis John D'Errico

PLEASE! Intelligent comments from all parties are valid and invited. But STOP the venomous comments, character assassination, insults, and what has been verging on libel.

ACT LIKE ADULTS, OR PROVE YOURSELVES TO BE SMALL CHILDREN.

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