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02122012, 09:38 PM #1
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 Feb 2012
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Need help with Math.pow Calculations
Hello again! Thanks for the help in the previous post I made last week. I'm in need of a little bit of assistance again.
I'm trying to get Math.pow to calculate and produce a result for my Mortgage Calculator project. I need to show a decreasing amount in the remaining balance of a mortgage loan. However the results I get seem to always stay the same. What am I doing wrong?
Code:import java.text.DecimalFormat; // This calculator will accurately calculate Mortgage Payments, while allowing for flexible variable adjustments //(i.e. Length of Payments, Principal, Interest.) Based on Service Request from McBride Financial // Author: Kenan Cross // public class MortgageCalculator { int i; // counter int termLimit = 30; int months; int payments; /* No. of monthly payments in mortgage*/ int monthsPd = 12 * i; //Calculations of months paid so far double balPd; //Part of Balance Paid Formula double balPd2; //Part of Balance Paid Formula double balPd3; //Part of Balance Paid formula double balPdCalc; //Calculated result of balPd and balPd2 double loanCalc; //Power of Calculation for compound interest double powCalc; //Power of calculation variable double rate; double loanBalance; double loanInterest; //Calculated Loan with Interest double newLoanBalance; //Calculated Remaining Loan Balanace double annualRate; //Computed Annual Rate double interestPlus; // rate + 1 double interestPd; // contains interest paid so far double interestAdj; double interestExp; int length; /* length of mortgage */ double principle; /* Principle loan amount */ double monthlyPayment; /* Calculated Monthly Payment */ DecimalFormat dec; DecimalFormat percentage; public static void main (String args[]){ MortgageCalculator calc = new MortgageCalculator(); calc.calculatePaymentAmount(); calc.printPaymentAmount(); } public MortgageCalculator(){ months = 12; rate = 0.0575; principle = 200000; length = 30; dec = new DecimalFormat ("$0.00"); percentage = new DecimalFormat("0.00%"); } public void calculatePaymentAmount(){ annualRate = ((rate)/(12)); payments = (months) * (length); interestAdj = (annualRate)+(1); interestPlus = (rate + 1); interestExp = Math.pow(interestAdj, payments); monthlyPayment = principle * (annualRate * interestExp)/(interestExp  1); loanCalc = principle * (Math.pow(interestAdj,(termLimit))); } //Above formula is based on M=P[i(1+i)^n]/[(1+i)^n1] found on ifitbreaks.com/interest.htm// public void printPaymentAmount (){ System.out.println("Your Loan Amount is "+ dec.format(principle)); System.out.println("Your Annual Rate is "+ percentage.format(rate)); System.out.println("Your monthly payment amount is " + dec.format (monthlyPayment)); System.out.println("Your principal balance with interest is " + dec.format (loanCalc)); for (i=1; i <= termLimit; i++){ //Loop set for the limit of Mortgage term powCalc = principle * (Math.pow(interestAdj, i))1; balPd = monthlyPayment/annualRate; balPd2 = balPd  principle; balPd3 = 1  Math.pow(annualRate, monthsPd); balPdCalc = balPd  (balPd2 * balPd3); //formula is based on Amt Paid = (L/R  P)[(1+R)^X  1] found // at http://www.infobarrel.com/Financial_Math:__Calculating_the_Mortgage_Balance_after_X_Number_of_Years interestPd = powCalc  principle; System.out.println("\tIn Year " + i + " you will have paid " + dec.format(interestPd) + " in interest."); System.out.println("\t Your remaining loan balance is " + dec.format(balPdCalc)); try { Thread.sleep(5000); } catch (InterruptedException e) { } } } }

02152012, 06:18 PM #2
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One thing that is happening is your monthsPd variable is being initialized at 12 * i; and never changes through each iteration. You want to move it into your for loop.
Code:for (i=1; i <= termLimit; i++){ //Loop set for the limit of Mortgage term monthsPd = 12 * i;
Code:double amtPaid = (monthlyPayment/annualRate  principle) * (Math.pow(1 + annualRate, monthsPd)  1); double mortgageBalance = loanCalc  amtPaid;
Code:System.out.println("\t Your remaining loan balance is " + dec.format(mortgageBalance));