Методы парабол

import matplotlib.pyplot as plt
import numpy as np

def F(x):
    return x**3 + 4*x**2 + 2*x + 1

def Par(a, b, eps, x, y):
    #метод парабол

    x1 = float(a)
    x2 = (a + b) / 2
    x3 = float(b)
    while not (x3 - x1) < eps:
        if x3 != x2 != x1 and x2 != x1:
            c1 = (F(x2) - F(x1)) / (x2 - x1)
            c2 = ((F(x3) - F(x1)) / (x3 - x1) - (F(x2) - F(x1)) / (x2 - x1)) / (x3 - x2)
            x_temp = (x1 + x2 - c1 / c2) / 2
            x_list = [x1, x2, x3, x_temp]
            x_list.sort()
            for i in range(2):
                if F(x_list[i]) >= F(x_list[i+1]) and F(x_list[i+1]) <=  F(x_list[i+2]):
                    x1 = x_list[i]
                    x2 = x_list[i+1]
                    x3 = x_list[i+2]
    print("Метод парабол: \nx* = ", (x1 + x3) / 2, "\ny_min = ", F((x1 + x3) / 2), '\n')

def main():
    a = -1
    b = 1
    eps = 0.01
    x = []
    y = []
    for i in np.arange(a, b, eps/10):
        x.append(i)
    y = [F(i) for i in x]
    plt.plot(x, y)
    plt.grid()
    plt.suptitle("Метод парабол")
    plt.show()
    Par(a, b, eps, x, y)

if __name__ == "__main__":
    main()