با سلام
دوستان عزیز برنامه زیر مقدار لاگرانژ رو محاسبه میکنه
#include <iostream.h>
#include <conio.h>
#include <stdlib.h>
void main()
{
float xi[100],fi[100],temp,li[100],x,p;
int i,n,j;
cout <<"enter number of sentences:\t";
cin >>n;
cout <<"enter value of x:\t";
cin >>x;
for (i=0;i<n;i++)
{
cout <<"enter xi["<<i<<"] :\t";
cin >>xi[i];
cout <<"enter fi["<<i<<"] :\t";
cin >>fi[i];
}//end of for
for (i=0;i<n;i++)
{
li[i]=1;
for (j=0;j<n;j++)
{
if(i==j)
continue;
li[i]*=(x-xi[j])/(xi[i]-xi[j]);
}//end of for
}//end of for
clrscr();
for (i=0;i<n;i++)
li[i]=li[i]*fi[i];
p=0;
for (i=0;i<n;i++)
p+=li[i];
cout <<"P"<<n-1<<"=\t"<<p;
getch();
}//end of program