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francois |
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//--------------------------------------------------------------------------- |
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#include <math.h> |
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#include <stdio.h> |
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#define EPS 3.0e-11 |
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#pragma hdrstop |
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#include "gestionversion.h" |
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#include "ot_quadrature_gauss.h" |
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//--------------------------------------------------------------------------- |
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#pragma package(smart_init) |
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void OT_QUADRATURE_GAUSS::gauss_legendre_points(double x1, double x2, double x[], double w[], int n) |
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{ |
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int m,j,i; |
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double z1,z,xm,xl,pp,p3,p2,p1; |
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m=(n+1)/2; |
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xm=0.5*(x2+x1); |
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xl=0.5*(x2-x1); |
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for (i=1;i<=m;i++) { |
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z=cos(M_PI*(i-0.25)/(n+0.5)); |
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do { |
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p1=1; |
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p2=0; |
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for (j=1;j<=n;j++) { |
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p3=p2; |
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p2=p1; |
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p1=((2*j-1)*z*p2-(j-1)*p3)/j; |
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} |
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pp=n*(z*p1-p2)/(z*z-1); |
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z1=z; |
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z=z1-p1/pp; |
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} while (fabs(z-z1) > EPS); |
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x[i]=xm-xl*z; |
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x[n+1-i]=xm+xl*z; |
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w[i]=2*xl/((1-z*z)*pp*pp); |
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w[n+1-i]=w[i]; |
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} |
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} |
