lagrange.cpp

Contains many numerical algorithms for interpolation.

//Lagrange's interpolation formula

#include<stdio.h>
#include<conio.h>
main()
{
 float x[20],y[20],p1,p2,s,xv;
 int n,i,j;
 printf("How many sets of values do you want to give:");
 scanf("%d",&n);
 for(i=0;i<n;i++)
 {
 	printf("Enter x%d,y%d:",i+1,i+1);
   scanf("%f%f",&x[i],&y[i]);
 }
 label:
 printf("\nEnter the value of x:");
 scanf("%f",&xv);
 s=0;
 for(j=0;j<n;j++)
 {
 	p1=y[j];
   p2=1;
  	for(i=0;i<n;i++)
 	{
   	if(i!=j)
	   {
   	 	p1=p1*(xv-x[i]);
         p2=p2*(x[j]-x[i]);
      }
   }
   s=s+(p1/p2);
 }
 printf("The value of y is:%f\n",s);
 printf("\nDo you want to continue(y/n):");
 if('y'==getch())
 	goto label;
}