using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var results = new List<List<double>>();

        var set = new double[] { 1, 2, -3 };

        GetCombinations(set.Where(x => x > 0).ToArray(), results);

        results.Add(set.Where(x => x > 0).ToList());

        var negatives = set.Where(x => x < 0).ToList();

        foreach (var negative in negatives)

        {

            var matches = results.Where(x => x.Sum(t => t) == -negative).ToList();

            foreach (var match in matches)

            {

                Console.WriteLine(string.Join(" + ", match) + " = " + negative);

            }

        }

    }

    private static void GetCombinations<T>(T[] set, List<List<T>> result)

    {

        for (int i = 0; i < set.Length; i++)

        {

            var temp = new List<T>(set.Where((s, index) => index != i));

​

            if (temp.Count > 0 && !result.Where(l => l.Count == temp.Count).Any(l => l.SequenceEqual(temp)))

            {

                result.Add(temp);

                GetCombinations<T>(temp.ToArray(), result);

            }

        }

    }

}