! test_permute.f90  test generating all permutations of vector

program test_permute
  implicit none
  integer, parameter :: sz = 10
  double precision, dimension(sz,sz) :: A
  integer, dimension(sz) :: vector, permuter
  integer :: last
  integer :: i, j, k, n

  interface
    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_permute.f90'
  n = 1
  do while(n .lt. 5)
    print *, 'initializing, n=',n
    do i=1,n
      vector(i) = i
      permuter(i) = n+1
    end do ! i
    print *, ' '
    print *, 'permutations for n=',n
    last = 0
    do while(last .eq.0)
      last = permute(n, vector, permuter)
      do i=1,n
        print *, 'Vector(',i,')=', vector(i),' , per=',permuter(i)
      end do ! i
    end do ! while
    n=n+1
  end do ! while
  print *, 'finished test_permute.f90'
end program test_permute