! test_permanent.f90  compute permanent of a matrix n!*n^2 flops

program test_permanent
  implicit none
  integer, parameter :: sz = 20
  double precision, dimension(sz,sz) :: A
  double precision :: perm
  integer :: last
  integer :: i, j, k, n

  ! for timing
  double precision :: start, now, next
  character*20 :: start_date
  character*20 :: start_time
  integer :: clock_count, clock_rate, clock_max

  interface
    double precision function permanent(n, sz, A)
      integer, intent(in) :: n, sz
      double precision, dimension(sz,sz), intent(in) :: A
    end function permanent
    double precision function udrnrt()
    end function udrnrt
    function permute(n, vector, permuter) result(last)
      integer, intent(in) :: n  ! number of items to permute
      integer, dimension(1:*), intent(inout) :: vector, permuter
      integer :: last
    end function permute 
  end interface

  print *, 'test_permanent.f90'
  ! for timing
  call date_and_time(date=start_date, time=start_time);
  print *, 'start_date=', start_date(5:6), '/', start_date(7:8), '/', start_date(1:4)
  print *, 'start_time=', start_time(1:2), ':', start_time(3:4), ':', start_time(5:10)
  call system_clock(count=clock_count, count_rate=clock_rate, count_max=clock_max)
  print *, 'clock_count=', clock_count, ', clock_rate=', clock_rate, ', clock_max=', clock_max
  start = (1.0D0+clock_count)/clock_rate
  print *, ' '

  n = 1
  do while(n .le. 12)
    print *, 'initializing, n=',n
    do i=1,n
      do j=1,n
          A(i,j) = udrnrt()
          if(n .le. 4) then
            print *, 'A(',i,',',j,')=',A(i,j)
          end if
      end do ! j
    end do ! i
    call system_clock(count=clock_count)
    now = (1.0D0+clock_count)/clock_rate
    perm = permanent(n, sz, A)
    call system_clock(count=clock_count)
    next = (1.0D0+clock_count)/clock_rate
    print *, 'permanent = ',perm,' in ',next-now, ' seconds'
    n=n+1
  end do ! while
  print *, ' '
  print *, 'flops are n * n!'
  print *, 'finished test_permanent.f90'
end program test_permanent