PROGRAM GAUSS_90
      REAL, allocatable ::  A(:,:), X(:), Y(:), START(:)
      INTEGER :: i
      character*10 time

      REAL TEMP
      REAL, allocatable :: SWAP(:)

      INTEGER j, n, location, location_array(1)

      print *, "Problem size = ? (>5)"
      read (*,*) n
      print *, "Problem size = ", n
      call date_and_time(time=time)
      print *, time, "     ---- time to start the job"
      allocate(a(n,n), x(n), y(n), start(n), swap(n))
      A = 0.1
      DO i=1,n
        START(i) = i
        A(1+MODULO(i+1,n),i) = i+5
      ENDDO
      Y = 0
      DO i = 1, n
        Y(i) = SUM( A(i,:)*START )
      ENDDO

      call date_and_time(time=time)
      print *, time, "     ---- problem has been set up"

      !CALL GAUSS_ELIM_90( A, X, Y )

       DO i = 1, n-1

! Between here >>
!-------------------------------------------------+
         location_array = MAXLOC( ABS(A(i:n,i)) ) !
         location = location_array(1)+i-1         !
         SWAP(i:n) = A(location,i:n)              !
         TEMP = Y(location)                       !
         IF (location /= i) THEN                  !
           A(location,i:n) = A(i,i:n)             !
           A(i,i:n) = SWAP(i:n)                   !
           Y(location) = Y(i)                     !
           Y(i) = TEMP                            !
         END IF                                   !
!-------------------------------------------------+
! << and here

         DO j = i+1, n
            A(j,i) = A(j, i) / swap(i)
            A(j, i+1:n) = A(j, i+1:n ) - a(j, i) * SWAP(i+1:n)
            Y(j) = Y(j) - a(j,i) * TEMP
         ENDDO
       ENDDO

       call date_and_time(time=time)
       print *, time, "     ---- forward finished "

       X(n) = Y(n) / A(n,n)
       DO i = n-1, 1, -1
         Y(1:i) = Y(1:i) - X(i+1) * A(1:i, i+1)
         X(i) = Y(i) / A(i,i)
       ENDDO

      call date_and_time(time=time)
      print *, time, "     ---- problem has been solved"

      DO i = 1, 5
        WRITE(*,*) i, X(i)
      ENDDO

      DO i = n - 4, n
        WRITE(*,*) i, X(i)
      ENDDO

      END PROGRAM GAUSS_90