Lagrange’s Interpolation
#include<stdio.h>
#include<conio.h>
int main ()
{
int n,i,j;
float x[10],f[10],fp,lf=1.0,sum=0.0,xp;
printf("input number of data points[n]: ");
scanf ("%d",&n);
printf("Input data points x(i) and value f(i) [one set in each line]: ");
for(i=1;i<=n;i++)
scanf("%f%f",&x[i],&f[i]);
printf("\nInput X at which interpolation is required: ");
scanf("%f",&xp);
for(i=1;i<=n;i++)
{
lf=1.0;
for (j=1;j<=n;j++)
{
if(i!=j)
lf=lf*(xp-x[j])/(x[i]-x[j]);
}
sum=sum+lf*f[i];
}
fp=sum;
printf("Lagragian interpolation at x=%f is %f ",xp,fp);
getch();
}