Not ending decimal error even when using MathContext

Question

I am creating code to implement this algorithm:

However, I get this error, even with MathContext (1000):

Exception in thread "main" java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result. at java.math.BigDecimal.divide(BigDecimal.java:1603) at picalculator.PiCalculator.calculatePi(PiCalculator.java:59) at picalculator.PiCalculator.main(PiCalculator.java:25) Java Result: 1 

When using this method:

 public static void calculatePi() { BigInteger firstFactorial; BigInteger secondFactorial; BigInteger firstMultiplication; BigInteger firstExponent; BigInteger secondExponent; int firstNumber = 1103; BigInteger firstAddition; BigDecimal currentPi = BigDecimal.ONE; BigDecimal pi = BigDecimal.ONE; BigDecimal one = BigDecimal.ONE; int secondNumber = 2; double thirdNumber = Math.sqrt(2.0); int fourthNumber = 9801; BigDecimal prefix = BigDecimal.ONE; for(int i=1;i<4;i++){ firstFactorial = factorial(4*i); secondFactorial = factorial(i); firstMultiplication = BigInteger.valueOf(26390*i); firstExponent = exponent(secondFactorial, 4); secondExponent = exponent(BigInteger.valueOf(396),4*i); firstAddition = BigInteger.valueOf(firstNumber).add(firstMultiplication); currentPi = currentPi.add(new BigDecimal(firstFactorial.multiply(firstAddition)).divide(new BigDecimal(firstExponent.multiply(secondExponent)), new MathContext(10000))); } prefix =new BigDecimal(secondNumber*thirdNumber); prefix = prefix.divide(new BigDecimal(fourthNumber), new MathContext(1000)); currentPi = currentPi.multiply(prefix, new MathContext(1000)); pi = one.divide(currentPi); System.out.println("Pi is: " + pi); return; } 

I proved that factorial (a); and the exponents (a, b) precisely believe the factorial a and the result a ^ b, respectively.

Does anyone know how to fix this?

Answer 1

You need

 pi = one.divide(currentPi, new MathContext(1000)); 

Since the result is almost certainly a repeating decimal number.

Consider

 BigDecimal a = new BigDecimal("4"); BigDecimal b = new BigDecimal("3"); BigDecimal c = a.divide(b) // java.lang.ArithmeticException: Non-terminating decimal expansion BigDecimal c = a.divide(b, new MathContext(10)); // No exception 

Answer 2

You might want to use a different version of divide . This gives you more control over the final scale returned by BigDecimal. Whereas with your version, the final scale depends on the scale of the dividend and divisor.

 int scale = 3; BigDecimal result = ONE.divide(new BigDecimal("3"), scale, RoundingMode.HALF_UP); // result is 0.333