Mathematical constant e generator in Java
Posted on April 30, 2003
A small class to generate the mathematical constant "e". Complete with timer and digits per second clock. Unpolished. Here's a quick benchmark and you can see that it doesn't scale.
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Date;/**
* calculate mathmatical constant e
*/public class ECalculator {
private static final int numberOfDigits = 1000;
public static void main(String[] args) {
ECalculator myEClass = new ECalculator();
System.out.println("Calculating e to " + numberOfDigits + " digits ...\n");
Date start = new Date();
BigDecimal e = myEClass.doCalculation();
Date stop = new Date();
long elapsedSeconds = (stop.getTime()-start.getTime()) / 1000;
System.out.println("e is: \n" + e);
if (elapsedSeconds
May 1st, 2003 - 15:57
Try this optimization
(Forgive the formatting)
// — Add a constant variable
public static final BigInteger BIG_INT_CONSTANT = BigInteger.valueOf(i);
/* the useful stuff */
private BigDecimal doCalculation()
{
BigInteger factorialTotal = new BigInteger(“1″);
BigDecimal bigE = new BigDecimal(“1″);
for (int i = 0; i < numberOfDigits; i++)
{
/*
* The Following adheres to the formula:
*
* e = 1/0! + 1/1! + 1/2! + 1/3! + 1/4! + …
*
*/
// increment factorial by multiplying itself by itself
factorialTotal = factorialTotal.add(
factorialTotal.multiply(BIG_INT_CONSTANT));
// — ^^^^^^^^^^^^^ Use the constant variable
// e grows and becomes more accurate
bigE = bigE.add(
BIG_INT_CONSTANT.divide(new BigDecimal(factorialTotal), numberOfDigits, BigDecimal.ROUND_HALF_UP));
// — ^^^^^^^^^ Use the BigInteger parameter constructor
}
return bigE;
}