from __future__ import print_function
from math import sqrt

# Oppgave a
def secant(f, x0, x1, N):
    xpp = x0
    xp = x1
    for i in range(N):
        x = xp - ((xp-xpp)/(f(xp)-f(xpp)))*f(xp)
        xpp = xp
        xp = x
    return x

# Oppgave b

#def f(x):
#    return x*x-2

def test_secant():
    x0 = 3.0
    x1 = 2.0
    f = lambda x: x*x - 2
    N = 10
    x = secant(f, x0, x1, N)

    success = abs(x - sqrt(2)) <= 1E-8
    msg = "Did not find the root sqrt(2) for the function x*x-2"
    assert success, msg

test_secant()