src/examples/console/MortgageCalculator.groovy

   1 /**
   2  * Mortgage Calculator
   3  * @author: Jeremy Rayner
   4  * based on algorithms by Jeff Louie, Dr W Carlini and Newton
   5  */
   6
   7 println "__..::~~'''~~::..__"
   8 println "Mortgage Calculator"
   9 println "~~~~~~~~~~~~~~~~~~~"
  10 println "Please input 3 of the 4 values in your mortgage calculation"
  11 println "This program will then calculate the value you leave blank"
  12 println ""
  13
  14 def variables = [
  15     "Amount of mortgage" : 0.0,
  16     "Annual interest rate (%)" : 0.0,
  17     "Loan duration (months)" : 0.0,
  18     "Monthly payments" : 0.0
  19 ]
  20
  21 for (entry in variables.entrySet()) {
  22     print("${entry.key}:")
  23     def userInput = System.in.readLine()
  24     if ("" == userInput) {
  25         valueToCalculate = entry.key
  26     } else {
  27         entry.value = userInput.toDouble()
  28     }
  29 }
  30
  31 println "$valueToCalculate = ${calculateValueOf(valueToCalculate)}"
  32
  33
  34
  35
  36
  37 def calculateValueOf(valueToCalculate) {
  38     def result = 0
  39     def principal = variables["Amount of mortgage"]
  40     def interest = variables["Annual interest rate (%)"] / 1200
  41     def months = variables["Loan duration (months)"]
  42     def payment = variables["Monthly payments"]
  43
  44     switch (valueToCalculate) {
  45     case "Amount of mortgage":
  46         result = 1 + interest
  47         result = 1/Math.pow(result,months)
  48         result = ((1-result)/interest) * payment
  49         break
  50     case "Loan duration (months)":
  51         result = (1 - (principal * interest / payment))
  52         result = Math.log(result)
  53         result = - result / Math.log(1 + interest)
  54         break
  55     case "Monthly payments":
  56         result = 1 + interest
  57         result = 1 / Math.pow(result,months)
  58         result = (principal * interest) / (1 - result)
  59         break
  60     case "Annual interest rate (%)":
  61         result = payment / principal
  62         def diff = 100; def accuracy = 0.00001; def maxIterations = 1000
  63         def index = 0
  64         while ((diff > accuracy) && (index < maxIterations)) {
  65             def temp = result
  66             def numerator = (principal * temp / payment) + Math.pow((1 + temp), -months) - 1
  67             def denominator= (principal / payment) - months * Math.pow((1 + temp), (-months - 1))
  68             result = temp - (numerator / denominator)
  69             diff = result - temp
  70             diff = Math.abs(diff)
  71             index++
  72         }
  73         result *= 1200
  74         break
  75     }
  76     return result
  77 }