program lu_main
       implicit none
       integer n, np, i, j
       parameter (np=10)
       integer indx(np)       
       real a(np,np), b(np), d
       character*40 filename1, filename2

       write (*,*)'Please tell me the dimension n of the matrix A(n,n):'
       read (*,*) n

       write (*,*) 'Please give the file name that contains A :'
       read (*,*) filename1
       write (*,*) 'Please give the file name that contains b :'
       read (*,*) filename2

       open (unit=20, file=filename1)
       do i=1,n
         read (20,*) ( a(i,j), j=1,n )
       enddo
       close(20)

       open (unit=20, file=filename2)
       do i=1,n
         read (20,*) b(i)
       enddo
       close(20)
       
       call ludcmp(a,n,np,indx,d)

       call lubksb(a,n,np,indx,b)
 
       write (*,*) 'The solution matrix is :'
       do i=1,n
         write (*,*) b(i)
       enddo

       do i=1,n
         d = d * a(i,i)
       end do
       write(*,*) 'The determinant is', d

       end