org.nd4j.linalg.util.Factorial Maven / Gradle / Ivy
/*-
*
* * Copyright 2015 Skymind,Inc.
* *
* * Licensed 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.nd4j.linalg.util;
/**
*
* @author dmtrl
*/
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.List;
/**
* Factorials.
*/
class Factorial {
/**
* The list of all factorials as a vector.
*/
static List a = new ArrayList<>();
/**
* ctor().
* Initialize the vector of the factorials with 0!=1 and 1!=1.
*/
public Factorial() {
if (a.isEmpty()) {
a.add(BigInteger.ONE);
a.add(BigInteger.ONE);
}
}
/**
* Compute the factorial of the non-negative integer.
*
* @param n the argument to the factorial, non-negative.
* @return the factorial of n.
*/
public BigInteger at(int n) {
while (a.size() <= n) {
final int lastn = a.size() - 1;
final BigInteger nextn = BigInteger.valueOf(lastn + 1);
a.add(a.get(lastn).multiply(nextn));
}
return a.get(n);
}
} /* Factorial */