# Numerical Methods: Interpolation with unequal interval with Lagrange’s method in C

Source Code:

///Interpolation with unequal intervals with Lagrange's Formula
#include <stdio.h>
#include <math.h>
#include <windows.h>
COORD coord = {0, 0};
void gotoxy (int x, int y)
{
coord.X = x; coord.Y = y; // X and Y coordinates
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
}
int main(){
float ax[20], ay[20], xp, yp = 0, dr, nr;
int no_data, i, j;
printf("How many data? ");
scanf("%d", &no_data);
printf("Enter Data: ");
for(i =0; i < no_data; i++){
gotoxy(1,2+i); printf("X%d: ", i+1);
scanf("%f", &ax[i]);
gotoxy(10, 2+i);printf("Y%d: ", i+1);
scanf("%f", &ay[i]);
}
printf("\nEnter value of x to find corresponding y ");
scanf("%f", &xp);
for(i = 0; i < no_data; i++){
dr = 1;
nr = 1;
for(j = 0; j<no_data; j++){
if(i!=j){
nr *= xp - ax[j];
dr *= ax[i] - ax[j];
}
}
yp += nr/dr*ay[i];
}
printf("\nrequired value of y is: %f", yp);
return 0;
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