Bisection Search

Possible Duplicate: Using bisection search to determine I have posted other thread but it did not receive answers thus i'm trying to provide some of my work to make more clear.

Solution 1:

This is the correct one.

originalBalance = 320000
annualInterestRate = 0.2
monthly_interest = annualInterestRate / 12
low = originalBalance/12
high = (originalBalance*(1 + monthly_interest)**12)/12
epsilon = 0.01
min_payment = (high + low)/2.0

while min_payment*12 - originalBalance >= epsilon:
    for month in range(0, 12):
        balance = (originalBalance - min_payment)/10 * (1+monthly_interest)

    if balance < 0:
        low = min_payment
    elif balance > 0:
        high = min_payment
        min_payment = (high + low)/2.0
print "lowest payment: " + str(balance)

Solution 2:

This is what you need

while abs(x) > epsilon:
    x = balance
    for month in range(0, 12):
        x = (x - ans) * (1+monthly_interest)