ip_back.c

包括线性插值

/* Note:Your choice is C IDE */
double Ip_back(double x[13],double y[13],double b[13],int n,double t)
{
 int i,k,m;
 double Ip,hi,p,q;
  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;
    hi=(x[m]-x[k]);
    p=x[m]-t;
    q=t-x[k];
    Ip=(b[k]/(6*hi)*pow(p,3))+(b[m]/(6*hi)*pow(q,3))+(y[k]/hi-(b[k]/6)*hi)*p+(y[m]/hi-(b[m]/6)*hi)*q;
    return Ip;
}