Description
Returns the natural logarithm of n!.
License
Open Source License
Parameter
Parameter | Description |
---|
n | argument |
Exception
Parameter | Description |
---|
IllegalArgumentException | if preconditions are not met. |
Return
n!
Declaration
public static double factorialLog(final int n)
Method Source Code
//package com.java2s;
/*//from w w w . j a v a 2 s .c o m
* Copyright (c) 2006-2011 Karsten Schmidt
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* http://creativecommons.org/licenses/LGPL/2.1/
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
*/
public class Main {
/** All long-representable factorials */
private static final long[] factorials = new long[] { 1, 1, 2, 6, 24,
120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600,
6227020800l, 87178291200l, 1307674368000l, 20922789888000l,
355687428096000l, 6402373705728000l, 121645100408832000l,
2432902008176640000l };
/**
* Returns the natural logarithm of n!.
* <p>
* <Strong>Preconditions</strong>:
* <ul>
* <li> <code>n >= 0</code> (otherwise
* <code>IllegalArgumentException</code> is thrown)</li>
* </ul></p>
*
* @param n argument
* @return <code>n!</code>
* @throws IllegalArgumentException if preconditions are not met.
*/
public static double factorialLog(final int n) {
if (n < 0) {
return 0;
}
if (n < 21) {
return Math.log(factorial(n));
}
double logSum = 0;
for (int i = 2; i <= n; i++) {
logSum += Math.log(i);
}
return logSum;
}
/**
* Returns n!. Shorthand for <code>n</code> <a
* href="http://mathworld.wolfram.com/Factorial.html"> Factorial</a>, the
* product of the numbers <code>1,...,n</code>.
* <p>
* <Strong>Preconditions</strong>:
* <ul>
* <li> <code>n >= 0</code> (otherwise
* <code>IllegalArgumentException</code> is thrown)</li>
* <li> The result is small enough to fit into a <code>long</code>. The
* largest value of <code>n</code> for which <code>n!</code> <
* Long.MAX_VALUE</code> is 20. If the computed value exceeds <code>Long.MAX_VALUE</code>
* an <code>ArithMeticException </code> is thrown.</li>
* </ul>
* </p>
*
* @param n argument
* @return <code>n!</code>
* @throws ArithmeticException if the result is too large to be represented
* by a long integer.
* @throws IllegalArgumentException if n < 0
*/
public static long factorial(final int n) {
if (n < 0) {
return 0;
}
if (n > 20) {
return 0;
}
return factorials[n];
}
}
Related
- factorial(long num)
- factorialAsDouble(int n)
- factorialAsDoubleIncludeDivisor(int n, double divisor)
- factorialCheckBounds(int n)
- factorialDouble(final int n)
- factorialLog(final int n)