Mathematical constant e generator in Java

by Dillon at 11pm, Apr 30th, 2003 in Java

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

Comments

James
Posted on 1st May, 2003

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;
}

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