48 lines
796 B
C
48 lines
796 B
C
|
|
#include <math.h>
|
|
#include "nrutil.h"
|
|
#define TINY 1.0e-25
|
|
#define FREERETURN {free_vector(d,1,n);free_vector(c,1,n);return;}
|
|
|
|
void ratint(xa,ya,n,x,y,dy)
|
|
float *dy,*y,x,xa[],ya[];
|
|
int n;
|
|
{
|
|
int m,i,ns=1;
|
|
float w,t,hh,h,dd,*c,*d;
|
|
|
|
c=vector(1,n);
|
|
d=vector(1,n);
|
|
hh=fabs(x-xa[1]);
|
|
for (i=1;i<=n;i++) {
|
|
h=fabs(x-xa[i]);
|
|
if (h == 0.0) {
|
|
*y=ya[i];
|
|
*dy=0.0;
|
|
FREERETURN
|
|
} else if (h < hh) {
|
|
ns=i;
|
|
hh=h;
|
|
}
|
|
c[i]=ya[i];
|
|
d[i]=ya[i]+TINY;
|
|
}
|
|
*y=ya[ns--];
|
|
for (m=1;m<n;m++) {
|
|
for (i=1;i<=n-m;i++) {
|
|
w=c[i+1]-d[i];
|
|
h=xa[i+m]-x;
|
|
t=(xa[i]-x)*d[i]/h;
|
|
dd=t-c[i+1];
|
|
if (dd == 0.0) nrerror("Error in routine ratint");
|
|
dd=w/dd;
|
|
d[i]=c[i+1]*dd;
|
|
c[i]=t*dd;
|
|
}
|
|
*y += (*dy=(2*ns < (n-m) ? c[ns+1] : d[ns--]));
|
|
}
|
|
FREERETURN
|
|
}
|
|
#undef TINY
|
|
#undef FREERETURN
|