[Scilab-users] {EXT} need a more efficient and faster code: suggestions welcome

[Claus Futtrup]

For me it's fun to see thevarious attempts at improving speed. Thanks to
Stephane for the x*x tip being better than x^2.

Best regards
Claus

On Feb 1, 2018 17:11, "Stéphane Mottelet" <stephane.mottelet at utc.fr> wrote:

> Hi all,
>
> I hope that the following will stop the (useless) competition : if speed
> is a real bottleneck for this particular computation, using plain C is the
> only option. The self-contained script (n=20000) given at the end of this
> message gives the following timings on various hardware (only one processor
> core is used) :
>
> 2,8 GHz Quad-Core Intel Xeon : 1.08 s (OSX)
> 2.2 GHz Xeon(R) CPU E5-2660 v2 @  : 1.84 s (Linux)
>
> Don't use plain Scilab if speed is a crucial issue....
>
> //  start of code
> source=['#include <math.h>'
> '#define SQR(x) ((x)*(x))'
> '#define MIN(x, y) (((x) < (y)) ? (x) : (y))'
> 'void mindist(double d[],double x[],int *n) {'
> '  int i,j,k;'
> '  double dist;'
> '  for (i=0;i<*n;i++) { '
> '    d[i]=INFINITY;'
> '    for (j=0;j<*n;j++) if (i!=j) { '
> '      dist=0;'
> '      for (k=0;k<3;k++) dist+=SQR(x[j*3+k]-x[i*3+k]);'
> '      d[i]=MIN(d[i],dist);'
> '    }'
> '  }'
> '}']
> mputl(source,'mindist.c')
> ilib_for_link('mindist','mindist.c',[],"c");
> exec loader.sce
>
> n=20000;
> r=23;
> radius = r*grand(n,1,'def').^(1/3);
> phi = 2*%pi*grand(n,1,'def');
> costheta = 1 - 2*grand(n,1,'def');
> radsintheta = radius.*sin(acos(costheta));
>
> X=[radsintheta.*cos(phi) radsintheta.*sin(phi) radius.*costheta];
>
> n=size(X,1);
> tic;
> dist=sqrt(call("mindist",X',2,"d",n,3,"i","out",[1,n],1,"d"));
> disp(toc())
> // end of code
>
> Le 31/01/2018 à 23:31, Rafael Guerra a écrit :
>
>> Hi Heinz,
>>
>> Find herein a vectorised memory hog solution for Scilab 6, which is fast
>> (~30 s for 20K points on Win7 laptop):
>>
>> // START OF CODE (Scilab 6)
>> Clear
>> n=20000;
>> r=23;
>> radius = r*grand(n,1,'def').^(1/3);
>> phi = 2*%pi*grand(n,1, 'def');
>> costheta = 1 - 2*grand(n,1, 'def');
>> radsintheta = radius.*sin(acos(costheta));
>> X = [radsintheta.*cos(phi), radsintheta.*sin(phi), radius.*costheta];
>> tic;
>> X2 = sum(X.*X, 'c');
>> X3 = X2.*.ones(n,1)';
>> X3 = X3 + X3';
>> D = abs(X3 - 2*(X*X'))';
>> D(1:n+1:$) = [];  // remove diagonal 0's
>> D = matrix(D,n-1,n); // reshape D to (n-1) x n size
>> MinDist1 = sqrt(min(D,'r'));
>> t1=toc();
>> disp(t1)
>> jj=-0.05:0.1:3.05;
>> H1 = histc(jj,MinDist1);
>> disp([0.05+jj(1:$-1)' H1']);
>> // END OF CODE
>>
>> Regards,
>> Rafael
>>
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>>
>
>
> --
> Stéphane Mottelet
> Ingénieur de recherche
> EA 4297 Transformations Intégrées de la Matière Renouvelable
> Département Génie des Procédés Industriels
> Sorbonne Universités - Université de Technologie de Compiègne
> CS 60319, 60203 Compiègne cedex
> Tel : +33(0)344234688
> http://www.utc.fr/~mottelet
>
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