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38 lines
809 B
C
38 lines
809 B
C
#define NRANSI
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#include <stdio.h>
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#include <stdlib.h>
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#include "nrutil.h"
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void spline(double x[], double y[], int n, double yp1, double ypn, double y2[])
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{
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int i,k;
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double p,qn,sig,un,*u;
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u=dvector(1,n-1);
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if (yp1 > 0.99e30)
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y2[1]=u[1]=0.0;
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else {
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y2[1] = -0.5;
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u[1]=(3.0/(x[2]-x[1]))*((y[2]-y[1])/(x[2]-x[1])-yp1);
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}
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for (i=2;i<=n-1;i++) {
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sig=(x[i]-x[i-1])/(x[i+1]-x[i-1]);
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p=sig*y2[i-1]+2.0;
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y2[i]=(sig-1.0)/p;
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u[i]=(y[i+1]-y[i])/(x[i+1]-x[i]) - (y[i]-y[i-1])/(x[i]-x[i-1]);
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u[i]=(6.0*u[i]/(x[i+1]-x[i-1])-sig*u[i-1])/p;
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}
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if (ypn > 0.99e30)
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qn=un=0.0;
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else {
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qn=0.5;
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un=(3.0/(x[n]-x[n-1]))*(ypn-(y[n]-y[n-1])/(x[n]-x[n-1]));
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}
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y2[n]=(un-qn*u[n-1])/(qn*y2[n-1]+1.0);
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for (k=n-1;k>=1;k--)
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{
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y2[k]=y2[k]*y2[k+1]+u[k];
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}
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free_dvector(u,1,n-1);
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}
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#undef NRANSI
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