# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt

x=np.array([0,2,3],float)
y=np.array([7,11,28],float)
                            #[-1]:means use the last value of the series.[2] can also be used.
xplt=np.linspace(x[0],x[-1],13)#linspace: Returns evenly spaced numbers 
print(xplt)                          #(between the start and end points) at the specified range.
yplt=np.array([],float)  #Calculated values will be added. Variable limits are used.
print(yplt)

for xp in xplt:
    yp=0        #Reference point. When -1 or +1 is used, 
                #the graph is moved on the y axis.
                      
    for xi,yi in zip(x,y):  
        yp +=yi*np.prod((xp-x[x !=xi])/(xi-x [x !=xi]))
    yplt= np.append(yplt,yp)  #is used to determine the values and their 
                                #position in the graph.

                                       
plt.plot(x,y,'bs',xplt,yplt,'r--') #bs: (b:blue)color and (s:square)shape of the spot
plt.xlabel('x')                     #r--: (r:red), (--)line shape.(.)(-)...
plt.ylabel('y')
plt.grid()
plt.show()