Using Bisection Search on Lowest Payments on Credit Card debt and

Question

My code:

monthlyInterestRate = annualInterestRate/12.0 
low = balance/12 
high = (balance*(1+monthlyInterestRate)**12)/12 
guess = (low+high)/2 
unpaidBalance = balance 
month = 1

while True:
    unpaidBalance= unpaidBalance-guess 
        while month < 13:
            if unpaidBalance <= -0.1:
                low = guess
                month += 1
            elif unpaidBalance >= 0.1:
                high = guess
                month += 1
            else:
                break
            guess = (low + high)/2 
print "Lowest Payment: " + str(round(guess, 2))

When I test it it gets stuck at the line "while month < 13:"

Why does it do this and how do I fix it?

Menagerie

what does it means for you that it gets stuck? ... – Competent

It loops at that line. – Menagerie

Search 'MITx' on stackoverflow to find other people with similar homework problem :) – Senega

Answer 1

If you break at each loop of inner while, you remains less than 13.

And this goes on and on since you proceed While True and do not update your guess.

I fear you are facing infinite looping there.

Your break statement breaks the closest loop, that is the While month < 13 loop. The next line is not read. guessis not updated. The while True is not broken.

Maybe you wanted to say

while month < 13:
   unpaidBalance= unpaidBalance-guess 
   if unpaidBalance <= -0.1:
         low = guess
   elif unpaidBalance >= 0.1:
         high = guess
   month += 1
   guess = (low + high)/2 

Competent

I just copied over the code (^^) to try it out, but that is still looping at the same line...??? – Menagerie

because you always fall in your else case. Month is not incremented, you remain below 13. Then, you should rework algorithm. – Competent

I'm still so confused! What am I supposed to do exactly? – Menagerie

try with my last update, then month is ALWAYS incremented and it should work. BUT it all depends of what you want in the end. – Competent

Here's a test case: annualInterestRate = 0.18 and balance = 999999, result should be 90325.07. – Menagerie

is that yours https://mcmap.net/q/1329775/-bisection-search-duplicate?rq=1 ? – Competent

No, it's not mine but it's the same problem. Thanks for all your help though! ~{^U^}~ – Menagerie

Answer 2

here you are

No is the best solution, but it works

monthlyPaymentRate = (balance*annualInterestRate/12)/((1-(1+annualInterestRate/12)**-12))

interest = monthlyPaymentRate * (annualInterestRate/12)

#print (monthlyPaymentRate)
#print (interest)
monthlyPaymentRate = (monthlyPaymentRate - interest) +1
#print (monthlyPaymentRate)
balanceInit = balance

epsilon = 0.01
low = monthlyPaymentRate
while low*12 - balance > epsilon:
    balances = balanceInit
    for i in range(12):
                 minpay =  monthlyPaymentRate
                 unpaybal = balances - minpay
                 interest = (annualInterestRate /12) * unpaybal
                  smontfinal =  unpaybal + interest
                  balances = smontfinal
                 #print('Remaining balance: ' ,round(balances,2) )
                 if balances <0:
                     low = -1
                     break
    if balances < 0 :
        low = -1
    else:
        monthlyPaymentRate =monthlyPaymentRate + 0.001 

print('Lowest Payment:' ,round(monthlyPaymentRate,2) )

Serve