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Thread: Using BigDecimal for Mathematical Formulas

  1. #1
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    Question Using BigDecimal for Mathematical Formulas

    I am simply confused on how to convert the equation below for bigDecimal objects. I have already tried this, and this and the output is really weird once I call the method.
    The first block of code is what I'm trying to convert into BigDecimal arithmetic.

    public static double calculateFutureValue(double monthlyInvestment,
    double monthlyInterestRate, int months)
    {
    double futureValue = 0;
    for (int i = 1; i <= months; i++)
    {
    futureValue =
    (futureValue + monthlyInvestment) *
    (1 + monthlyInterestRate);
    // System.out.println("Month: " + i + " FutureValue: " + futureValue);
    }
    return futureValue;
    }
    }

    My attempt at this is as follows:

    public static BigDecimal calculateFutureValue(double monthlyInvestment,
    double monthlyInterestRate, int months)
    {
    BigDecimal futureValue = new BigDecimal(0.0);
    BigDecimal montlyInvestmentDecimal = new BigDecimal(monthlyInvestment);
    BigDecimal montlyInterestRateDecimal = new BigDecimal(monthlyInterestRate);
    BigDecimal one = new BigDecimal(1.0);
    for (int i = 1; i <= months; i++)
    {
    futureValue = (futureValue.add(futureValue)).multiply
    (one.add(montlyInterestRateDecimal));
    System.out.println("Month: " + i + " FutureValue: " + futureValue);
    }
    return futureValue;
    }

    Output:
    Welcome to the Future Value Calculator

    DATA ENTRY
    Enter monthly investment: 1
    Enter yearly interest rate: .01
    Enter number of years: 3
    Month: 1 FutureValue: 0E-66
    Month: 2 FutureValue: 0E-132
    Month: 3 FutureValue: 0E-198
    Month: 4 FutureValue: 0E-264
    Month: 5 FutureValue: 0E-330
    Month: 6 FutureValue: 0E-396
    Month: 7 FutureValue: 0E-462
    Month: 8 FutureValue: 0E-528
    Month: 9 FutureValue: 0E-594
    Month: 10 FutureValue: 0E-660
    Month: 11 FutureValue: 0E-726
    Month: 12 FutureValue: 0E-792
    Month: 13 FutureValue: 0E-858
    Month: 14 FutureValue: 0E-924
    Month: 15 FutureValue: 0E-990
    Month: 16 FutureValue: 0E-1056
    Month: 17 FutureValue: 0E-1122
    Month: 18 FutureValue: 0E-1188
    Month: 19 FutureValue: 0E-1254
    Month: 20 FutureValue: 0E-1320
    Month: 21 FutureValue: 0E-1386
    Month: 22 FutureValue: 0E-1452
    Month: 23 FutureValue: 0E-1518
    Month: 24 FutureValue: 0E-1584
    Month: 25 FutureValue: 0E-1650
    Month: 26 FutureValue: 0E-1716
    Month: 27 FutureValue: 0E-1782
    Month: 28 FutureValue: 0E-1848
    Month: 29 FutureValue: 0E-1914
    Month: 30 FutureValue: 0E-1980
    Month: 31 FutureValue: 0E-2046
    Month: 32 FutureValue: 0E-2112
    Month: 33 FutureValue: 0E-2178
    Month: 34 FutureValue: 0E-2244
    Month: 35 FutureValue: 0E-2310
    Month: 36 FutureValue: 0E-2376

    FORMATTED RESULTS
    Monthly investment: $1.00
    Yearly interest rate: 0.0%
    Number of years: 3
    Future value: 0E-2376

    Continue? (y/n):

    So clearly this still isn't working. Can anybody help?


  2. #2
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    Default Re: Using BigDecimal for Mathematical Formulas

    0E-66 means that you have a decimal places zero of 66 digits. like 12.666666666666666666666... (66 digits of decimal digits) whose value when multiply by zero is 0 (any number multiply by zero is zero).
    example big decimal value of 3.200000000000000177635683940025046467781066894531 25 multiply by zero will result of 0E-50 means 0.0000000000000000000000000000000000000000

    futureValue = (futureValue.add(futureValue)).multiply
    (one.add(montlyInterestRateDecimal));


    your futureValue is zero and any number multiply by zero is zero. you even have futureValue.add(futureValue), that would be 0 + 0, still 0.

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