Обьясните как это работает? - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace Lab_6
{
    class Mtrx
    {
        double[,] matrix;
        int n, m;
        public int N
        {
            get{return n;}
        }
        public int M
        {
            get { return M; }
        }
        public Mtrx (int n, int m)
        {
            this.n = n;
            this.m = m;
            matrix=new double[n,m];
            Random r = new Random();
            for (int i=0;i<n;i++)
                for (int j=0;j<m;j++)
                {       
                    matrix[i, j] = r.Next(0,100);
                }
        }
        public double this[int n, int m]
        {
            get {return matrix[n,m];}
            set { matrix[n, m] = value; }
        }
        public void showmatrix()
        {
            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                    Console.Write("{0} ", matrix[i, j]);
                Console.WriteLine();
            }
        }
        public void showpodmatrix(int n, int m)
        {
            for (int i = 0; i < n; i++)
            {
                for (int j = 0; j < m; j++)
                    Console.Write("{0} ", matrix[i, j]);
                Console.WriteLine();
            }
        }
        public void changeN(int n)
        {
            double[,] tempM=new double[this.n,m];
            tempM=matrix;
            matrix = new double[n, m];
            int tmp=this.n*m;
            for (int i=0;i<n;i++)           
                for (int j = 0; j < m; j++)
                    if (tmp != 0 && i<=this.n) { matrix[i, j] = tempM[i, j]; tmp--; }
                    else matrix[i, j] = 0;
            
        }
        public void changeM(int m)
        {
            double[,] tempM = new double[n, this.m];
            tempM = matrix;
            matrix = new double[n, m];
            int tmp = n * this.m;
            for (int i = 0; i < n; i++)
                for (int j = 0; j < m; j++)
                    if (tmp != 0 && i <= this.m) { matrix[i, j] = tempM[i, j]; tmp--; }
                    else matrix[i, j] = 0;
 
        }
 
    }
}