import matplotlib.pyplot as plt
import numpy as np

def f(x):
    return (x - 1)**2 + 3

# Senterdifferans:
def dfdx(f_vec, dx):
    deriverte = np.zeros(len(f_vec)) + np.nan
    for i in range(1, len(f_func)-1, 1):
        deriverte[i] = (f_vec[i+1] - f_vec[i-1])/(2*dx)
    return deriverte 

dx = 0.001
x_start = 0.0
x_stop = 3.0
N = int ((x_stop - x_start)/dx + 1)
x_koor = np.linspace(x_start, x_stop, N)

f_func = f(x_koor)
f_derivert = dfdx(f_func, dx)

#  Plotting:

plt.plot(x_koor, f_derivert, 'b')
plt.grid()
plt.xlabel('x')
plt.ylabel('df_dx')

# plt.savefig('plot_der_int_senterdiff.pdf')
plt.show()