57 lines
1.1 KiB
C++
57 lines
1.1 KiB
C++
#include <cmath>
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#include "nr.h"
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using namespace std;
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void NR::tqli(Vec_IO_DP &d, Vec_IO_DP &e, Mat_IO_DP &z)
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{
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int m,l,iter,i,k;
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DP s,r,p,g,f,dd,c,b;
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int n=d.size();
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for (i=1;i<n;i++) e[i-1]=e[i];
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e[n-1]=0.0;
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for (l=0;l<n;l++) {
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iter=0;
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do {
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for (m=l;m<n-1;m++) {
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dd=fabs(d[m])+fabs(d[m+1]);
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if (fabs(e[m])+dd == dd) break;
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}
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if (m != l) {
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if (iter++ == 30) nrerror("Too many iterations in tqli");
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g=(d[l+1]-d[l])/(2.0*e[l]);
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r=pythag(g,1.0);
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g=d[m]-d[l]+e[l]/(g+SIGN(r,g));
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s=c=1.0;
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p=0.0;
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for (i=m-1;i>=l;i--) {
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f=s*e[i];
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b=c*e[i];
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e[i+1]=(r=pythag(f,g));
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if (r == 0.0) {
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d[i+1] -= p;
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e[m]=0.0;
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break;
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}
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s=f/r;
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c=g/r;
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g=d[i+1]-p;
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r=(d[i]-g)*s+2.0*c*b;
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d[i+1]=g+(p=s*r);
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g=c*r-b;
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// Next loop can be omitted if eigenvectors not wanted
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for (k=0;k<n;k++) {
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f=z[k][i+1];
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z[k][i+1]=s*z[k][i]+c*f;
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z[k][i]=c*z[k][i]-s*f;
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}
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}
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if (r == 0.0 && i >= l) continue;
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d[l] -= p;
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e[l]=g;
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e[m]=0.0;
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}
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} while (m != l);
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}
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}
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