Bisection search in Python cant find the answer? Why does it result in negative balance?











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This code get down to -73535 and exits the loop. I can't figure out what's wrong.



balance = 999999   

annualInterestRate = 0.18   

epsilon = 0.05



monthlyInterestRate = annualInterestRate / 12    

lowerBound = balance / 12    

upperBound = (balance * ((1 + monthlyInterestRate)**12)) / 12.0    

print(upperBound, lowerBound)   

currentBalance = balance    

middle = (upperBound + lowerBound) / 2   



while abs(round(upperBound - lowerBound,2)) >= epsilon:    

    currentBalance = balance

    for i in range(12):

        unpaidBalance = currentBalance - middle

        currentBalance= unpaidBalance - (monthlyInterestRate * unpaidBalance)

    print(currentBalance)

    if abs(unpaidBalance) < 0.05:

        print("hahaha")

        break

    elif currentBalance < 0:

        upperBound = middle

    elif currentBalance > 0:

        lowerBound = middle

    middle = (upperBound + lowerBound) / 2





python payment bisection







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  • 2




    In future, I would recommend following the PEP8 Style Guide as it is much more readable. Specifically, take a look at Naming conventions and whitespace in expressions and statements.
    – Modelmat
    Nov 7 at 8:44










  • Can you explain the meaning of the value you are apparently trying to converge, perhaps with a reference to the algorithm?
    – tripleee
    Nov 7 at 10:19










  • This is to try to figure out the minimum lowest payment I need to pay every month to pay off my credit card debt.I have to use bisection search.
    – Debora
    Nov 8 at 5:49















up vote
0
down vote

favorite












This code get down to -73535 and exits the loop. I can't figure out what's wrong.



balance = 999999   

annualInterestRate = 0.18   

epsilon = 0.05



monthlyInterestRate = annualInterestRate / 12    

lowerBound = balance / 12    

upperBound = (balance * ((1 + monthlyInterestRate)**12)) / 12.0    

print(upperBound, lowerBound)   

currentBalance = balance    

middle = (upperBound + lowerBound) / 2   



while abs(round(upperBound - lowerBound,2)) >= epsilon:    

    currentBalance = balance

    for i in range(12):

        unpaidBalance = currentBalance - middle

        currentBalance= unpaidBalance - (monthlyInterestRate * unpaidBalance)

    print(currentBalance)

    if abs(unpaidBalance) < 0.05:

        print("hahaha")

        break

    elif currentBalance < 0:

        upperBound = middle

    elif currentBalance > 0:

        lowerBound = middle

    middle = (upperBound + lowerBound) / 2





python payment bisection







share|improve this question




















  • 2




    In future, I would recommend following the PEP8 Style Guide as it is much more readable. Specifically, take a look at Naming conventions and whitespace in expressions and statements.
    – Modelmat
    Nov 7 at 8:44










  • Can you explain the meaning of the value you are apparently trying to converge, perhaps with a reference to the algorithm?
    – tripleee
    Nov 7 at 10:19










  • This is to try to figure out the minimum lowest payment I need to pay every month to pay off my credit card debt.I have to use bisection search.
    – Debora
    Nov 8 at 5:49













up vote
0
down vote

favorite









up vote
0
down vote

favorite











This code get down to -73535 and exits the loop. I can't figure out what's wrong.



balance = 999999   

annualInterestRate = 0.18   

epsilon = 0.05



monthlyInterestRate = annualInterestRate / 12    

lowerBound = balance / 12    

upperBound = (balance * ((1 + monthlyInterestRate)**12)) / 12.0    

print(upperBound, lowerBound)   

currentBalance = balance    

middle = (upperBound + lowerBound) / 2   



while abs(round(upperBound - lowerBound,2)) >= epsilon:    

    currentBalance = balance

    for i in range(12):

        unpaidBalance = currentBalance - middle

        currentBalance= unpaidBalance - (monthlyInterestRate * unpaidBalance)

    print(currentBalance)

    if abs(unpaidBalance) < 0.05:

        print("hahaha")

        break

    elif currentBalance < 0:

        upperBound = middle

    elif currentBalance > 0:

        lowerBound = middle

    middle = (upperBound + lowerBound) / 2





python payment bisection







share|improve this question















This code get down to -73535 and exits the loop. I can't figure out what's wrong.



balance = 999999   

annualInterestRate = 0.18   

epsilon = 0.05



monthlyInterestRate = annualInterestRate / 12    

lowerBound = balance / 12    

upperBound = (balance * ((1 + monthlyInterestRate)**12)) / 12.0    

print(upperBound, lowerBound)   

currentBalance = balance    

middle = (upperBound + lowerBound) / 2   



while abs(round(upperBound - lowerBound,2)) >= epsilon:    

    currentBalance = balance

    for i in range(12):

        unpaidBalance = currentBalance - middle

        currentBalance= unpaidBalance - (monthlyInterestRate * unpaidBalance)

    print(currentBalance)

    if abs(unpaidBalance) < 0.05:

        print("hahaha")

        break

    elif currentBalance < 0:

        upperBound = middle

    elif currentBalance > 0:

        lowerBound = middle

    middle = (upperBound + lowerBound) / 2





python payment bisection




python payment bisection






share|improve this question















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edited Nov 7 at 19:36









halfer

14.2k757105




14.2k757105










asked Nov 7 at 8:33









Debora

41




41








  • 2




    In future, I would recommend following the PEP8 Style Guide as it is much more readable. Specifically, take a look at Naming conventions and whitespace in expressions and statements.
    – Modelmat
    Nov 7 at 8:44










  • Can you explain the meaning of the value you are apparently trying to converge, perhaps with a reference to the algorithm?
    – tripleee
    Nov 7 at 10:19










  • This is to try to figure out the minimum lowest payment I need to pay every month to pay off my credit card debt.I have to use bisection search.
    – Debora
    Nov 8 at 5:49














  • 2




    In future, I would recommend following the PEP8 Style Guide as it is much more readable. Specifically, take a look at Naming conventions and whitespace in expressions and statements.
    – Modelmat
    Nov 7 at 8:44










  • Can you explain the meaning of the value you are apparently trying to converge, perhaps with a reference to the algorithm?
    – tripleee
    Nov 7 at 10:19










  • This is to try to figure out the minimum lowest payment I need to pay every month to pay off my credit card debt.I have to use bisection search.
    – Debora
    Nov 8 at 5:49








2




2




In future, I would recommend following the PEP8 Style Guide as it is much more readable. Specifically, take a look at Naming conventions and whitespace in expressions and statements.
– Modelmat
Nov 7 at 8:44




In future, I would recommend following the PEP8 Style Guide as it is much more readable. Specifically, take a look at Naming conventions and whitespace in expressions and statements.
– Modelmat
Nov 7 at 8:44












Can you explain the meaning of the value you are apparently trying to converge, perhaps with a reference to the algorithm?
– tripleee
Nov 7 at 10:19




Can you explain the meaning of the value you are apparently trying to converge, perhaps with a reference to the algorithm?
– tripleee
Nov 7 at 10:19












This is to try to figure out the minimum lowest payment I need to pay every month to pay off my credit card debt.I have to use bisection search.
– Debora
Nov 8 at 5:49




This is to try to figure out the minimum lowest payment I need to pay every month to pay off my credit card debt.I have to use bisection search.
– Debora
Nov 8 at 5:49

















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