36 lines
695 B
C
36 lines
695 B
C
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#include <math.h>
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#include "nrutil.h"
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void qrdcmp(a,n,c,d,sing)
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float **a,*c,*d;
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int *sing,n;
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{
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int i,j,k;
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float scale,sigma,sum,tau;
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*sing=0;
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for (k=1;k<n;k++) {
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scale=0.0;
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for (i=k;i<=n;i++) scale=FMAX(scale,fabs(a[i][k]));
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if (scale == 0.0) {
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*sing=1;
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c[k]=d[k]=0.0;
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} else {
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for (i=k;i<=n;i++) a[i][k] /= scale;
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for (sum=0.0,i=k;i<=n;i++) sum += SQR(a[i][k]);
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sigma=SIGN(sqrt(sum),a[k][k]);
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a[k][k] += sigma;
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c[k]=sigma*a[k][k];
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d[k] = -scale*sigma;
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for (j=k+1;j<=n;j++) {
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for (sum=0.0,i=k;i<=n;i++) sum += a[i][k]*a[i][j];
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tau=sum/c[k];
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for (i=k;i<=n;i++) a[i][j] -= tau*a[i][k];
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}
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}
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}
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d[n]=a[n][n];
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if (d[n] == 0.0) *sing=1;
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}
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