aalgrg.c

程序为五个一元插值算法

double aalgrg(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);
    }
  i=0;
  while ((x[i]<t)&&(i<n))i=i+1;
  k=i-4;
  if(k<0)k=0;
  m=i+3;
  if(m>n-1)m=n-1;
  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);
}