File: bisection.py

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import math
def func(x):
	return x**3 - 10.0* x*x + 5

def bisect(f, x1, x2, epsilon=1.0e-9):
    f1 = f(x1)
    f2 = f(x2)
    if f1*f2 > 0.0: 
	print 'x1 ans x2 are on the same side of x-axis'
	return None
    n = math.ceil(math.log(abs(x2 - x1)/epsilon)/math.log(2.0))
    n = int(n)
    for i in range(n):
        x3 = 0.5 * (x1 + x2)
	f3 = f(x3)
        if f3 == 0.0: return x3
        if f2*f3 < 0.0:
             x1 = x3
	     f1 = f3
        else:
             x2 =x3
             f2 = f3
    return (x1 + x2)/2.0


print bisect(func, 0.70, 0.8, 1.0e-4)
print bisect(func, 0.70, 0.8, 1.0e-9)