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  1. import java.math.BigDecimal;
  2. import java.math.RoundingMode;
  3.  
  4. class Calculo {
  5.  
  6.     private static final BigDecimal CEM = new BigDecimal(100);
  7.     private static final BigDecimal DOIS = new BigDecimal(2);
  8.  
  9.     private static final int PRECISAO_CALCULO = 21;
  10.     private static final int PRECISAO_FINAL = 5;
  11.  
  12.     private static final BigDecimal DELTA =
  13.             BigDecimal.ONE.divide(BigDecimal.TEN.pow(PRECISAO_FINAL));
  14.  
  15.     private static final BigDecimal financiamento(int n, BigDecimal j, BigDecimal p) {
  16.         BigDecimal a = BigDecimal.ONE.add(j).pow(n);
  17.  
  18.         BigDecimal b = BigDecimal.ONE.divide(
  19.                 a,
  20.                 PRECISAO_CALCULO,
  21.                 RoundingMode.HALF_EVEN);
  22.  
  23.         return BigDecimal.ONE
  24.                 .subtract(b)
  25.                 .multiply(p)
  26.                 .divide(j, PRECISAO_CALCULO, RoundingMode.HALF_EVEN);
  27.     }
  28.  
  29.     private static final BigDecimal taxaFinanciamento(
  30.             BigDecimal q0,
  31.             int n,
  32.             BigDecimal p)
  33.     {
  34.         BigDecimal j1 = DELTA;
  35.         BigDecimal j2 = BigDecimal.ONE;
  36.         BigDecimal q1 = financiamento(n, j1, p);
  37.         BigDecimal q2 = financiamento(n, j2, p);
  38.         BigDecimal m1 = q1.subtract(q0);
  39.         BigDecimal m2 = q2.subtract(q0);
  40.         if (m1.abs().compareTo(DELTA) <= 0) return j1;
  41.         if (m2.abs().compareTo(DELTA) <= 0) return j2;
  42.         for (int i = 0; i < 50; i++) {
  43.             if (m1.signum() == m2.signum()) {
  44.                 throw new ArithmeticException("Fora do intervalo"
  45.                         + ": q1=[" + q1 + "], j1=[" + j1 + "], m1=[" + m1 + "]"
  46.                         + ", q2=[" + q2 + "], j2=[" + j2 + "], m2=[" + m2 + "]"
  47.                         + ", i=" + i);
  48.             }
  49.             BigDecimal j3 = j1.add(j2).divide(DOIS);
  50.             BigDecimal q3 = financiamento(n, j3, p);
  51.             BigDecimal m3 = q3.subtract(q0);
  52.             if (m3.abs().compareTo(DELTA) <= 0) return j3;
  53.             if (m3.signum() == m1.signum()) {
  54.                 q1 = q3;
  55.                 j1 = j3;
  56.             } else {
  57.                 q2 = q3;
  58.                 j2 = j3;
  59.             }
  60.         }
  61.         throw new ArithmeticException("Não convergiu"
  62.                 + ": q1=[" + q1 + "], j1=[" + j1 + "], m1=[" + m1 + "]"
  63.                 + ", q2=[" + q2 + "], j2=[" + j2 + "], m2=[" + m2 + "]");
  64.     }
  65.  
  66.     private static void teste(int q0, int p, int n) {
  67.         BigDecimal bdq0Ideal = new BigDecimal(q0);
  68.         BigDecimal bdp = new BigDecimal(p);
  69.         BigDecimal j = taxaFinanciamento(bdq0Ideal, n, bdp);
  70.         BigDecimal bdq0Obtido = financiamento(n, j, bdp);
  71.         System.out.println("----------");
  72.         System.out.println("q0-ideal=[" + bdq0Ideal + "]");
  73.         System.out.println("p=[" + bdp + "]");
  74.         System.out.println("j=[" + j + "]");
  75.         System.out.println("q0-obtido=[" + bdq0Obtido + "]");
  76.         System.out.println("----------");
  77.         System.out.println();
  78.     }
  79.  
  80.     public static void main(String[] args) {
  81.         teste(750, 86, 10);
  82.         teste(750, 85, 10);
  83.     }
  84. }
Success #stdin #stdout 0.1s 2841600KB
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----------
q0-ideal=[750]
p=[86]
j=[0.025690244208984076976776123046875]
q0-obtido=[749.999997639096753068406]
----------

----------
q0-ideal=[750]
p=[85]
j=[0.023429261477030813694000244140625]
q0-obtido=[749.999996056141438963093]
----------
https://ideone.com/H5MUsP
language:
Java (HotSpot 12)
created:
6 years ago
visibility:
public

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