program main

!*****************************************************************************80
!
!! MAIN is the main program for L1_NORM.
!
  use omp_lib

  integer n
  parameter ( n = 1000 )
 
  integer i
  integer num_threads
  double precision wtime
  double precision wtime1
  double precision wtime2
  real x(n,n)
  real x_l1_norm(n)

!$omp parallel
  num_threads = omp_get_num_threads ( )
!$omp end parallel

  write ( *, * ) ' '
  write ( *, * ) 'L1_NORM'
  write ( *, * ) '  FORTRAN90 version'
  write ( *, * ) '  Number of threads available is ', num_threads
!
!  Set X to random values.
!
  call random_number ( harvest = x(1:n,1:n) )
!
!  Compute sequentially.
!
  wtime1 = omp_get_wtime ( )
  do j = 1, n
    x_l1_norm(j) = 0.0
    do i = 1, n
      x_l1_norm(j) = x_l1_norm(j) + abs ( x(i,j) )
    end do
  end do
  wtime2 = omp_get_wtime ( )
  wtime = wtime2 - wtime1

  write ( *, * ) ' '
  write ( *, * ) 'Sequential calculation using a loop:'
  write ( *, * ) '  L1_NORM (first 4 ) = ', x_l1_norm(1:4)
  write ( *, * ) '  Time =    ', wtime
!
!  Compute using a loop.
!
  wtime1 = omp_get_wtime ( )
!$omp parallel shared ( x, x_l1_norm ) private ( i, j )
!$omp do
  do j = 1, n
    x_l1_norm(j) = 0.0
    do i = 1, n
      x_l1_norm(j) = x_l1_norm(j) + abs ( x(i,j) )
    end do
  end do
!$omp end do
!$omp end parallel
  wtime2 = omp_get_wtime ( )
  wtime = wtime2 - wtime1

  write ( *, * ) ' '
  write ( *, * ) 'Parallel calculation, using a loop:'
  write ( *, * ) '  L1_NORM (first 4 ) = ', x_l1_norm(1:4)
  write ( *, * ) '  Time =    ', wtime
!
!  Compute sequentially using FORTRAN90 vector operations.
!
  wtime1 = omp_get_wtime ( )
  do j = 1, n
    x_l1_norm(j) = sum ( abs ( x(1:n,j) ) )
  end do
  wtime2 = omp_get_wtime ( )
  wtime = wtime2 - wtime1

  write ( *, * ) ' '
  write ( *, * ) 'Sequential calculation FORTRAN90 vector operations:'
  write ( *, * ) '  L1_NORM (first 4 ) = ', x_l1_norm(1:4)
  write ( *, * ) '  Time =    ', wtime
!
!  Compute using FORTRAN90 vector operations.
!
  wtime1 = omp_get_wtime ( )
!$omp parallel shared ( x, x_l1_norm ) private ( j )
!$omp do
  do j = 1, n
    x_l1_norm(j) = sum ( abs ( x(1:n,j) ) )
  end do
!$omp end do
!$omp end parallel

  wtime2 = omp_get_wtime ( )
  wtime = wtime2 - wtime1

  write ( *, * ) ' '
  write ( *, * ) 'Parallel calculation using FORTRAN90 vector operations:'
  write ( *, * ) '  L1_NORM (first 4 ) = ', x_l1_norm(1:4)
  write ( *, * ) '  Time =    ', wtime
  stop
end