src/input/bisection_v2.py

def bisection(f, a, b, eps):
    fa = f(a)
    if fa*f(b) > 0:
        return None, 0

    i = 0   # iteration counter
    while b-a > eps:
        i += 1
        m = (a + b)/2.0
        fm = f(m)
        if fa*fm <= 0:
            b = m  # root is in left half of [a,b]
        else:
            a = m  # root is in right half of [a,b]
            fa = fm
    return m, i


def f(x):
    return 2*x - 3   # one root x=1.5

eps = 1E-5
a, b = 0, 10
x, iter = bisection(f, a, b, eps)
if x is None:
    print 'f(x) does not change sign in [%g,%g].' % (a, b)
else:
    print 'The root is', x, 'found in', iter, 'iterations'
    print 'f(%g)=%g' % (x, f(x))