/*
* 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.
*/
package org.apache.commons.math4.util;
import org.apache.commons.math4.exception.NotPositiveException;
import org.apache.commons.numbers.gamma.LogGamma;
import org.junit.Assert;
import org.junit.Test;
/**
* Test cases for the {@link CombinatoricsUtils.FactorialLog} class.
*/
public class FactorialLogTest {
@Test(expected=NotPositiveException.class)
public void testPrecondition1() {
CombinatoricsUtils.FactorialLog.create().withCache(-1);
}
@Test(expected=NotPositiveException.class)
public void testNonPositiveArgument() {
final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create();
f.value(-1);
}
@Test
public void testDelegation() {
final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create();
// Starting at 21 because for smaller arguments, there is no delegation to the
// "LogGamma" class.
for (int i = 21; i < 10000; i++) {
final double expected = LogGamma.value(i + 1);
Assert.assertEquals(i + "! ",
expected, f.value(i), 0d);
}
}
@Test
public void testCompareDirectWithoutCache() {
// This test shows that delegating to the "Gamma" class will also lead to a
// less accurate result.
final int max = 100;
final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create();
for (int i = 0; i < max; i++) {
final double expected = factorialLog(i);
Assert.assertEquals(i + "! ",
expected, f.value(i), 2 * Math.ulp(expected));
}
}
@Test
public void testCompareDirectWithCache() {
final int max = 1000;
final CombinatoricsUtils.FactorialLog f = CombinatoricsUtils.FactorialLog.create().withCache(max);
for (int i = 0; i < max; i++) {
final double expected = factorialLog(i);
Assert.assertEquals(i + "! ",
expected, f.value(i), 0d);
}
}
@Test
public void testCacheIncrease() {
final int max = 100;
final CombinatoricsUtils.FactorialLog f1 = CombinatoricsUtils.FactorialLog.create().withCache(max);
final CombinatoricsUtils.FactorialLog f2 = f1.withCache(2 * max);
final int val = max + max / 2;
final double expected = factorialLog(val);
Assert.assertEquals(expected, f2.value(val), 0d);
}
@Test
public void testCacheDecrease() {
final int max = 100;
final CombinatoricsUtils.FactorialLog f1 = CombinatoricsUtils.FactorialLog.create().withCache(max);
final CombinatoricsUtils.FactorialLog f2 = f1.withCache(max / 2);
final int val = max / 4;
final double expected = factorialLog(val);
Assert.assertEquals(expected, f2.value(val), 0d);
}
// Direct implementation.
private double factorialLog(final int n) {
double logSum = 0;
for (int i = 2; i <= n; i++) {
logSum += FastMath.log(i);
}
return logSum;
}
}