LU factorization and inverse matrix

// Rozkład macierzy LU = PA

using System;
using System.IO;
using System.Globalization;
namespace LUdecomposition
{
    class LUdecomposition
    {
        public const double ZERO = 1.0e-15;
        public static void Main()
        {
            char esc;
            string str,path;
            int i,j,n;
            double[,] A;
            double[] b;
            int[] p;
            double d;
            NumberFormatInfo nfi = new NumberFormatInfo();
            nfi.NumberDecimalSeparator = ".";
            Console.WriteLine("Podaj ścieżkę do pliku w którym chcesz zapisać wynik");
            path = Console.ReadLine();
            using(StreamWriter sw = new StreamWriter(path,true))
            {
                do
                {
                    try
                    {
                        Console.Clear();
                        Console.WriteLine("Rozwiązywanie układów równań liniowych metodą rozkładu macierzy LU = PA");
                        Console.WriteLine();
                        Console.WriteLine("Podaj liczbę równań n=");
                        str = Console.ReadLine();
                        int.TryParse(str,out n);
                        A = new double[n,n];
                        b = new double[n];
                        p = new int[n];
                        for(i = 0;i < n;i++)
                        {
                            Console.WriteLine("Wprowadz " + (i+1).ToString(nfi) + ". wiersz macierzy");
                            for(j = 0;j < n;j++)
                            {
                                str = Console.ReadLine();
                                double.TryParse(str,out A[i,j]);
                            }
                            Console.WriteLine("Wprowadz " + (i+1).ToString(nfi) + ". wyraz wolny");
                            str = Console.ReadLine();
                            double.TryParse(str,out b[i]);
                        }
                        FactorLU(n,A,p,out d);
                        sw.WriteLine(d.ToString(nfi));
                        for(i = 0;i < n && Math.Abs(d) > ZERO  ;i++)
                        {
                            for(j = 0;j < n; j++)
                            {
                                Console.Write(A[i,j].ToString(nfi)+" , ");
                                sw.Write(A[i,j].ToString(nfi) + " , ");
                            }
                            Console.WriteLine();
                            sw.WriteLine();
                        }
                        if(Math.Abs(d) > ZERO)
                        {
                            SolveLU(n,A,p,b);
                            for(i = 0;i < n && Math.Abs(d) > ZERO ;i++)
                            {
                                Console.WriteLine(b[i].ToString(nfi));
                                sw.WriteLine(b[i].ToString(nfi));
                            }
                            Console.WriteLine();
                            sw.WriteLine();
                        }
                    }
                    catch(System.IndexOutOfRangeException e)
                    {

                    }
                    esc = (char)Console.ReadKey().Key;
                }
                while(esc != (char)ConsoleKey.Escape);
            }
        }
        public static void FactorLU(int n,double[,] A,int[] p,out double d)
        {
            int k,i,j,l;
            double pmax,tmp;
            d = 1.0;
            for(k = 0;k < n ;k++)
            {
                pmax = Math.Abs(A[k,k]);
                l = k;
                for(j = k + 1;j < n; j++)
                {
                    if(Math.Abs(A[j,k]) > pmax)
                    {
                        pmax = Math.Abs(A[j,k]);
                        l = j;
                    }
                }
                if(l != k)
                {
                    for(j = 0;j < n; j++)
                    {
                        tmp = A[k,j];
                        A[k,j] = A[l,j];
                        A[l,j] = tmp;
                    }
                    d = -d;
                }
                d *= A[k,k];
                if(pmax <= ZERO)
                    return ;
                p[k] = l;
                for(i = k + 1; i < n; i++)
                {
                    A[i,k]/=A[k,k];
                    for(j = k + 1;j < n; j++)
                        A[i,j] -= A[i,k]*A[k,j];
                }
            }
        }
        public static void SolveLU(int n,double[,] LU,int[] p,double[] b)
        {
            int i,k;
            double tmp;
            for(k = 0;k < n - 1; k++)
            {
                tmp = b[k];
                b[k] = b[p[k]];
                b[p[k]] = tmp;
            }
            for(k = 1;k < n; k++)
                for(i = 0; i < k; i++)
                    b[k] -= b[i]*LU[k,i];
            for(k = n - 1; k >= 0; k--)
            {
                for(i = k + 1;i < n; i++)
                    b[k] -= LU[k,i]*b[i];
                b[k] /= LU[k,k];
            }
        }
    }
}

// Macierz odwrotna

using System;
using System.IO;
using System.Globalization;
namespace MatrixInverse
{
    class MatrixInverse
    {
        public static void Main()
        {
            char esc;
            string str,path;
            int i,j,n;
            double[,] A;
            double d;
            NumberFormatInfo nfi = new NumberFormatInfo();
            nfi.NumberDecimalSeparator = ".";
            Console.WriteLine("Podaj ścieżkę do pliku w którym chcesz zapisać wynik");
            path = Console.ReadLine();
            using(StreamWriter sw = new StreamWriter(path,true))
            {
                do
                {
                    Console.Clear();
                    Console.WriteLine("Odwracanie macierzy");
                    Console.WriteLine();
                    Console.WriteLine("Podaj rozmiar macierzy n=");
                    str = Console.ReadLine();
                    int.TryParse(str,out n);
                    A = new double[n+1,2*n+1];
                    for(i = 1;i <= n;i++)
                    {
                        Console.WriteLine("Wprowadz " + i.ToString(nfi) + ". wiersz macierzy");
                        for(j = 1;j <= n;j++)
                        {
                            str = Console.ReadLine();
                            double.TryParse(str,out A[i,j]);
                        }
                    }
                    Inverse(A,n,out d);
                    sw.WriteLine(d.ToString(nfi));
                    for(i = 1;i <= n && d != 0.0 ;i++)
                    {
                        for(j = n + 1;j <= 2*n;j++)
                        {
                            Console.Write(A[i,j].ToString(nfi)+" , ");
                            sw.Write(A[i,j].ToString(nfi) + " , ");
                        }
                        Console.WriteLine();
                        sw.WriteLine();
                    }

                    esc = (char)Console.ReadKey().Key;
                }
                while(esc != (char)ConsoleKey.Escape);
            }
        }
        public static void Inverse(double[,] A,int n,out double d)
        {
            int i,j,k,m;
            double s,t,temp;
            d = 1.0;
            for(i = 1;i <= n;i++)
                for(j = n+1;j <= 2*n;j++)
                    if(i == j - n)
                        A[i,j] = 1.0;
                    else
                        A[i,j] = 0.0;
            for(i = 1;i <= n;i++)
            {
                m = i;
                for(j = i;j <= n;j++)
                    if(Math.Abs(A[j,i]) > Math.Abs(A[m,i]))
                        m = j;
                for(j = 1;j <= 2*n;j++)
                {
                    temp = A[i,j];
                    A[i,j] = A[m,j];
                    A[m,j] = temp;
                }
                if(m != i)
                    d = -d;
                if(A[i,i] == 0.0)
                {
                    d = 0.0;
                    return;
                }
                s = A[i,i];
                for(j = 1;j <= 2*n;j++)
                    A[i,j] /= s;
                for(j = i + 1;j <= n;j++)
                {
                    t = A[j,i];
                    for(k = i;k <= 2*n;k++)
                        A[j,k]-=A[i,k]*t;
                }
            }
            for(k = n + 1;k <= 2*n;k++)
            {
                for(i = n;i >= 1;i--)
                {
                    s = A[i,k];
                    for(j = i + 1;j <= n;j++)
                        s -= A[i,j]*A[j,k];
                    A[i,k] = s;
                }
            }
        }
    }
}