using System;
using System.Diagnostics;
using System.Threading;

namespace LU_cSharp
{
    class Program
    {
        static int THREAD_COUNT = 1;
        static int SIZE = 3;
        static double[] matrix = new double[SIZE * SIZE];

        static void Main(string[] args)
        {
            var rng = new Random();
            var sw = new Stopwatch();

            for (int i = 0; i < SIZE * SIZE; ++i)
            {
                matrix[i] = rng.Next(10) + 1;
            }

            sw.Start();

            var threads = new Thread[THREAD_COUNT];

            for (int i = 0; i < THREAD_COUNT; ++i)
            {
                threads[i] = new Thread(new ParameterizedThreadStart(LuDecompose));
                threads[i].Start(i);
            }
            for (int i = 0; i < THREAD_COUNT; ++i)
            {
                threads[i].Join();
            }
            sw.Stop();

            Console.WriteLine("L");
            for (int i = 0; i < SIZE; ++i)
            {
                for (int j = 0; j < SIZE; ++j)
                {
                    if (i > j)
                    {
                        Console.Write(matrix[i * SIZE + j] + "\t");
                    }
                    else if (i == j)
                    {
                        Console.Write(1.0 + "\t");
                    }
                    else
                    {
                        Console.Write(0.0 + "\t");
                    }
                }
                Console.WriteLine("");
            }

            Console.WriteLine("U");
            for (int i = 0; i < SIZE; ++i)
            {
                for (int j = 0; j < SIZE; ++j)
                {
                    if (i <= j)
                    {
                        Console.Write(matrix[i * SIZE + j] + "\t");
                    }
                    else
                    {
                        Console.Write(0.0 + "\t");
                    }
                }
                Console.WriteLine("");
            }


            Console.WriteLine("finished with " + THREAD_COUNT + " threads after: " + sw.ElapsedMilliseconds + " ms");

            Console.ReadKey();
        }

        public static void LuDecompose(object threadId)
        {
            int rowID;
            int workShare = SIZE / THREAD_COUNT;
            for (int columnID = workShare * (int)threadId; columnID < SIZE && columnID < workShare * ((int)threadId + 1); ++columnID)
            {
                for (rowID = columnID + 1; rowID < SIZE; rowID++)
                {
                    matrix[rowID * SIZE + columnID] /= matrix[columnID * SIZE + columnID];
                }

                for (rowID = columnID + 1; rowID < SIZE; rowID++)
                {
                    int innerColumnID;
                    double factor = matrix[rowID * SIZE + columnID];
                    for (innerColumnID = columnID + 1; innerColumnID < SIZE; innerColumnID++)
                    {
                        matrix[rowID * SIZE + innerColumnID] -= factor * matrix[columnID * SIZE + innerColumnID];
                    }
                }
            }
        }
    }
}