using System;

using System.Diagnostics;

using System.Text;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

        var rd = new Random();

        int minDim = 256*3/2;

        int maxDim = 512*3/2;

        int commonCount = rd.Next(minDim, maxDim);      

        var intMatrix1 = GenerateMatrix(rd.Next(minDim,maxDim), commonCount);

        var intMatrix2 = GenerateMatrix(commonCount, rd.Next(minDim,maxDim));

        var sw = new Stopwatch();

        sw.Start();

        var result = intMatrix1.ParallelMultiply(intMatrix2);       

        sw.Stop();

        Console.WriteLine($"Matrix parallel multiplication [{intMatrix1.RowCount}, {intMatrix1.ColumnCount}] x [{intMatrix2.RowCount}, {intMatrix2.ColumnCount}] tooks: {sw.Elapsed}");

        sw.Restart();

        result = intMatrix1.Multiply(intMatrix2);

        sw.Stop();

        Console.WriteLine($"Matrix multiplication [{intMatrix1.RowCount}, {intMatrix1.ColumnCount}] x [{intMatrix2.RowCount}, {intMatrix2.ColumnCount}] tooks: {sw.Elapsed}");

    }

    public static IntMatrix GenerateMatrix(int rowCount, int columnCount)

    {

        var result = new IntMatrix(rowCount, columnCount);

        var rd = new Random();

        for(int i=0; i<rowCount; i++)

        {

            for(int j=0; j<columnCount; j++)

            {

                result[i, j] = rd.Next(100)+1;

            }

        }

        return result;

    }

}

​

public class IntMatrix

{

    private int[,] items;

    public int RowCount {get; private set;}

    public int ColumnCount {get; private set;}

    public IntMatrix(int[,] items)

    {

        int row = items.GetLength(0);

        RowCount = row;

        int column = items.GetLength(1);

        ColumnCount = column;

        items = new int[row, column];

        for(int r=0; r<row; r++)

        {

            for(int c=0; c<column; c++)

            {

                this.items[r,c] = items[r,c];

            }

        }

    }

    public IntMatrix(int rowCount, int columnCount)

    {

        items = new int[rowCount, columnCount];

        RowCount = rowCount;

        ColumnCount = columnCount;

    }

    public int this[int row, int column]

    {

        get {return items[row, column];}

        set {items[row, column] = value;}

    }

    public IntMatrix Multiply(IntMatrix intMatrix)

    {

        if(intMatrix.RowCount != ColumnCount)

        {

            throw new ArgumentException();

        }

        var result = new IntMatrix(RowCount, intMatrix.ColumnCount);

        for(int r=0; r<RowCount; r++)

        {

            for(int c=0; c<intMatrix.ColumnCount; c++)

            {

                int total = 0;

                for(int i=0; i<ColumnCount; i++)

                {

                    total += this[r, i] * intMatrix[i, c];

                }

                result[r,c] = total;

            }

        }

        return result;

    }

    public IntMatrix ParallelMultiply(IntMatrix intMatrix)

    {

        if(intMatrix.RowCount != ColumnCount)

        {

            throw new ArgumentException();

        }

        var result = new IntMatrix(RowCount, intMatrix.ColumnCount);

        Parallel.For(0, RowCount, r=> {

            for(int c=0; c<intMatrix.ColumnCount; c++)

            {

                int total = 0;

                for(int i=0; i<ColumnCount; i++)

                {

                    total += this[r, i] * intMatrix[i, c];

                }

                result[r,c] = total;

            }

        });     

        return result;

    }

    public override string ToString()

    {

        var sb = new StringBuilder();

        for(int i=0; i<RowCount; i++)

        {

            for(int j=0; j<ColumnCount; j++)

            {

                sb.Append(this[i,j]);

                sb.Append(" ");

            }

            sb.AppendLine();

        }

        return sb.ToString();

    }

}