70 lines
1.2 KiB
C
70 lines
1.2 KiB
C
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#include <math.h>
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void tred2(float **a, int n, float d[], float e[])
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{
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int l,k,j,i;
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float scale,hh,h,g,f;
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for (i=n;i>=2;i--) {
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l=i-1;
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h=scale=0.0;
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if (l > 1) {
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for (k=1;k<=l;k++)
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scale += fabs(a[i][k]);
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if (scale == 0.0)
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e[i]=a[i][l];
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else {
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for (k=1;k<=l;k++) {
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a[i][k] /= scale;
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h += a[i][k]*a[i][k];
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}
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f=a[i][l];
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g=(f >= 0.0 ? -sqrt(h) : sqrt(h));
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e[i]=scale*g;
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h -= f*g;
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a[i][l]=f-g;
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f=0.0;
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for (j=1;j<=l;j++) {
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a[j][i]=a[i][j]/h;
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g=0.0;
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for (k=1;k<=j;k++)
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g += a[j][k]*a[i][k];
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for (k=j+1;k<=l;k++)
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g += a[k][j]*a[i][k];
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e[j]=g/h;
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f += e[j]*a[i][j];
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}
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hh=f/(h+h);
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for (j=1;j<=l;j++) {
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f=a[i][j];
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e[j]=g=e[j]-hh*f;
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for (k=1;k<=j;k++)
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a[j][k] -= (f*e[k]+g*a[i][k]);
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}
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}
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} else
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e[i]=a[i][l];
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d[i]=h;
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}
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d[1]=0.0;
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e[1]=0.0;
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/* Contents of this loop can be omitted if eigenvectors not
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wanted except for statement d[i]=a[i][i]; */
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for (i=1;i<=n;i++) {
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l=i-1;
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if (d[i]) {
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for (j=1;j<=l;j++) {
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g=0.0;
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for (k=1;k<=l;k++)
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g += a[i][k]*a[k][j];
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for (k=1;k<=l;k++)
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a[k][j] -= g*a[k][i];
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}
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}
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d[i]=a[i][i];
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a[i][i]=1.0;
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for (j=1;j<=l;j++) a[j][i]=a[i][j]=0.0;
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}
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}
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