mathnet-numerics/src/Numerics/Combinatorics.cs

// <copyright file="Combinatorics.cs" company="Math.NET">
// Math.NET Numerics, part of the Math.NET Project
// http://mathnet.opensourcedotnet.info
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namespace MathNet.Numerics
{
    using System;

    /// <summary>
    /// Enumerative Combinatorics and Counting.
    /// </summary>
    public static class Combinatorics
    {
        /// <summary>
        /// Computes the number of variations without repetition. The order matters and each object can be chosen only once.
        /// </summary>
        /// <param name="n">Number of elements in the set.</param>
        /// <param name="k">Number of elements to choose from the set. Each element is chosen at most once.</param>
        /// <returns>Maximum number of distinct variations.</returns>
        public static double Variations(int n, int k)
        {
            if (k < 0 || n < 0 || k > n)
            {
                return 0;
            }

            throw new NotImplementedException();
        }

        /// <summary>
        /// Computes the number of variations with repetition. The order matters and each object can be chosen more than once.
        /// </summary>
        /// <param name="n">Number of elements in the set.</param>
        /// <param name="k">Number of elements to choose from the set. Each element is chosen 0, 1 or multiple times.</param>
        /// <returns>Maximum number of distinct variations with repetition.</returns>
        public static double VariationsWithRepetition(int n, int k)
        {
            if (k < 0 || n < 0)
            {
                return 0;
            }

            return Math.Pow(n, k);
        }
    }
}