Mega Code Archive
Returns the natural logarithm of n!
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import java.io.File;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
public class Main {
/**
* Returns the natural logarithm of n!.
*
* <Strong>Preconditions</strong>:
* <ul>
* <li> <code>n >= 0</code> (otherwise
* <code>IllegalArgumentException</code> is thrown)</li>
* </ul>
*
* @param n argument
* @return <code>n!</code>
* @throws IllegalArgumentException if preconditions are not met.
*/
public static double factorialLog(final int n) {
if (n < 0) {
throw new IllegalArgumentException("must have n > 0 for n!");
}
double logSum = 0;
for (int i = 2; i <= n; i++) {
logSum += Math.log((double)i);
}
return logSum;
}
}
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