aclgrg.c

来自「程序为五个一元插值算法」· C语言 代码 · 共 35 行

#include"math.h"
double aclgrg(x,y,n,t)
int n;
double t,x[],y[];
{int i,j,k,m;
 double z,s;
 z=0.0;
 if(n<1)return(z);
 if(n==1){z=y[0];return(z);}
 if(n==2)
   {z=(y[0]*(t-x[1])-y[1]*(t-x[0]))/(x[0]-x[1]);
    return(z);
   }
 if (t<=x[1]){k=0;m=2;}
 else if(t>=x[n-2]){k=n-3;m=n-1;}
 else
   {k=1;m=n;
    while (m-k!=1)
     {i=(k+m)/2;
      if(t<x[i-1])m=i;
      else k=i;
     }
    k=k-1;m=m-1;
    if(fabs(t-x[k])<fabs(t-x[m]))k=k-1;
    else m=m+1;
   }
 z=0.0;
 for(i=k;i<=m;i++)
   {s=1.0;
    for(j=k;j<=m;j++)
      if(j!=i)s=s*(t-x[j])/(x[i]-x[j]);
    z=z+s*y[i];
   }
 return(z);
 }