lagrange(X,Y,Xa)

1 dimension Lagrange interpolation

The function finds the Lagrange polynomials that passes through the points (x1,y1), (x2,y2), ... (xn,yn).
It takes in parameter 3 variables:
X = [x1,x2,...xn]
Y= [y1,y2,...yn];
Xa : the point we want to calculate P(Xa).
it returns the Lagrange Polynomial (P) and P(Xa).