niudun.c

计算方法c牛顿插值函数

#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
double NEWT(int n,double *x,double *y,double t)
{
    int i,j;
    double *s,p;
    s=(double *)calloc(n+1,sizeof(double));
    if(s==NULL)
        exit(1);
    for(i=1;i<=n;i++)
        s[i]=y[i];
    for(j=1;j<=n-1;j++)
        for(i=n;i>=j+1;i--)
            s[i]=(s[i]-s[i-1])/(x[i]-x[i-1]);
    p=y[n];
    for(i=n-1;i>=1;i--)
        p=p*(t-x[i])+s[i];
    free(s);
    return (p);
}
double NEWT(int,double *,double *,double);
main()
{
   int n;
  double t,*x,*y;
  n=6;
  t=75.5;
  //printf("这是牛顿插值算法,请输入要计算的x值:");
  //scanf("%e",&t); 
  x=(double*)calloc(n+1,sizeof(double));
  if(x==NULL)
      exit(1);
  y=(double*)calloc(n+1,sizeof(double));
  if(y==NULL)
      exit(1);
  x[0]=75;
  x[1]=76;
  x[2]=77;
  x[3]=78;
  x[4]=79;
  x[5]=80;
  y[0]=2.768;
  y[1]=2.833;
  y[2]=2.903;
  y[3]=2.979;
  y[4]=3.062;
  y[5]=3.153;
  printf("使用牛顿插值算法:\n");
  printf("当x=75.5时,计算结果为: %f \n",NEWT(n,x,y,t));
  t=78.3;
  printf("当x=78.3时,计算结果为: %f \n",NEWT(n,x,y,t));
  free(x);
  free(y);
  return 0;
}