Calculates the multinomial coefficient. - Java java.lang

Java examples for java.lang:Math Calculation

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Description

Calculates the multinomial coefficient.

Demo Code

/*******************************************************************************
 * Copyright 2014 Felipe Takiyama/*  www .j a v  a 2  s  .  c  o m*/
 * 
 * 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.
 ******************************************************************************/
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.MathContext;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Main{
    /**
     * Calculates the 
     * <a href="https://en.wikipedia.org/wiki/Multinomial_coefficient#
     * Multinomial_coefficients">multinomial coefficient.</a>
     * 
     * @param m The multinomial to calculate
     * @return The value of the specified multinomial
     */
    public static BigInteger multinomial(Multinomial m) {
        BigInteger result = BigInteger.ONE;
        if (m.size() < 2 || m.isZeroed()) {
            result = BigInteger.ONE;
        } else {
            for (int i = 1; i < m.size(); i++) {
                int n = m.sumTerms(0, i);
                int k = m.get(i);
                BigInteger c = combination(n, k);
                result = result.multiply(c);
            }
        }
        return result;
    }
    /**
     * Calculates the binomial coefficient C(n,k).
     * <br>
     * This method returns 0 if n = 0 and k > 0. It throws an
     * IllegalArgumentException if any specified argument is negative.
     * 
     * @param n A nonnegative integer
     * @param k A nonnegative integer
     * @return The binomial coefficient C(n,k).
     * @throws IllegalArgumentException If the specified arguments are
     * negative (at least one of them)
     */
    public static BigInteger combination(int n, int k)
            throws IllegalArgumentException {

        if (n < 0 || k < 0) {
            throw new IllegalArgumentException(
                    "Cannot calculate combination"
                            + " for negative numbers.");
        }
        if (n == 0) {
            return BigInteger.ZERO;
        }

        BigInteger r = BigInteger.ONE;
        int nMinusK = n - k;
        for (int i = 1; i <= k; i++) {
            r = r.multiply(BigInteger.valueOf(nMinusK + i)).divide(
                    BigInteger.valueOf(i));
        }
        return r;
    }
}

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