分段抛物插值.c

数值分析的几个C实现,比较小.

#include<stdio.h>
#include<math.h>
#define n 5
main()
{int i,l,m;
double s=0,t,w=2.5;double x[n+1]={1,2,3,4,5,6},y[n+1]={1,4,9,16,25,36};
for(i=2;i<=n;i++)
  if(w<x[i])
   { if(fabs(x[i-1]-w)<fabs(x[i]-w))
       i--;
     break;
   }
for(m=i-1;m<=i+1;m++)
 { t=1;
   for(l=i-1;l<=i+1;l++)
   if(m!=l) t*=(w-x[l])/(x[m]-x[l]);
   s+=t*y[m];
 }
printf("%.6f\n",s);getch();
}