lab3(CM) ver 2.0

import matplotlib.pyplot as plt


def Lagrange(x, lst_x=[], lst_y=[]):
    F = 0
    for k in range(6):
        mult = 1
        for i in range(6):
            if i != k:
                mult = (x-lst_x[i])/(lst_x[k]-lst_x[i])*mult
        F += lst_y[k]*mult
    return(F)


lst_x = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]
lst_y = [5, 6, 8, 10, 12, 13, 12, 10, 8, 10, 8, 11, 7, 9, 11, 10, 9, 12, 11, 6]
lst_x_l = []
lst_y_l = []

x = 1
while x <= 3:
    lst_x_l.append(x)
    lst_y_l.append(Lagrange(x, lst_x[0:6], lst_y[0:6]))
    x += 0.25

i = 1
j = 0
while x <= 20:
    while x <= 4+j:
        lst_x_l.append(x)
        lst_y_l.append(Lagrange(x, lst_x[i:i+6], lst_y[i:i+6]))
        x += 0.25
    j += 1
    if i >= 14:
        i = 14
    else:
        i += 1

plt.plot(lst_x, lst_y, lst_x_l, lst_y_l)
plt.xticks(range(1, 22, 1))     # отметки на оси x от 1 до 21; шаг 2
plt.grid(linestyle='--', linewidth=0.5)
plt.title('Interpolation')
plt.xlabel('x')
plt.ylabel('f - исходная , F- полином Лагранжа')
plt.legend('fF', loc=4)
plt.show()