平分搜索導致無限循環

我想使用平分搜索來找出多少月付款應該是爲了支付用戶將輸入的12個月內的全部餘額。但是，我寫的這段代碼進入了無限循環，顯示出「低，高，montlyPayment無限次」。我不知道哪個代碼導致這個問題，因爲條件語句對我來說似乎是正確的。平分搜索導致無限循環

initialBalance = float(raw_input('Enter the outstanding balance on your   credit card')) 
annualInterestrate = float(raw_input('Enter the annual credit card interest rate as a decimal')) 
monthlyInterestrate = round(annualInterestrate, 2) 

balance = initialBalance 
while balance > 0: 
    numMonth = 0 
    balance = initialBalance 
    low = balance/12.0 
    high = (balance*(1+(annualInterestrate/12.0))**12.0)/12.0 
    epsilon = 0.01 
    monthlyPayment = round((high + low)/2.0, 2) 
    while abs(monthlyPayment*12.0 - initialBalance) >= epsilon: 
     print 'low =', low, 'high =', high, 'monthlyPayment =', round(monthlyPayment,2) 
     if monthlyPayment*12.0 < balance: 
      low = monthlyPayment 
     else: 
      high = monthlyPayment 
     monthlyPayment = round((high + low)/2.0, 2) 
     while balance > 0 and numMonth < 12: 
      numMonth += 1 
      interest = monthlyInterestrate * balance 
      balance -= monthlyPayment 
      balance += interest 
balance = round(balance, 2) 

print 'RESULT' 
print 'monthly payment to pay off debt in 1 year:', monthlyPayment 
print 'Number of months needed:', numMonth 
print 'Balance:',balance

來源

2016-07-07 K.heer

下聯：'餘額= initialBalance'。是設計還是偶然？ –

我想知道通過反覆試驗找出一個近似結果的重點是什麼，同時你可以逆轉公式並立即得到確切的結果？ – spectras

餘額= initialBalance是多餘的，但我不認爲這是造成這個問題的原因。這是我正在研究麻省理工學院開放課件的一個問題集，它指定了對分搜索的使用。 –

我已經重新編碼的上述問題，因爲在循環

balance = 120000 
annualInterestRate = 0.1 
rate=annualInterestRate/12.0 
high=(balance * (1 + rate)**12)/12.0 
low=balance/12.0 
payment=0 
bal_ref=balance 
unpaid=balance 
N=0 
while (abs(unpaid) > .01): 
    month=0 
    pay=(high+low)/2 
    balance=bal_ref 
    while(month < 12): 
     unpaid=balance-pay 
     balance=unpaid + (unpaid * rate) 
     month +=1 
    if (abs(unpaid) < .01): 
     payment=pay 
     break 
    elif (unpaid > .01): 
     low=pay 
    elif (unpaid < -.01): 
     high=pay 
    N+=1 
print("Payment:",round(pay,2))

來源

2017-06-17 13:57:55

請解釋一下，你改變了什麼。 – Ray

平分搜索導致無限循環

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