remove_self_loops Module Subroutine

  module subroutine remove_self_loops(this, indices)
    !! Remove self-loops from the graph.
    implicit none

    ! Arguments
    class(graph_type), intent(inout) :: this
    !! Parent. Instance of the graph structure.
    integer, dimension(:), intent(in), optional :: indices
    !! Indices of the vertices from which self-loops are removed.

    ! Local variables
      integer :: i, j
      !! Loop indices.

      if(this%num_edges .eq. 0)then
         write(0,*) 'No edges to remove self-loops from'
         return
      end if

      ! Remove self-loops in reverse order to maintain index validity
      do i = this%num_edges, 1, -1
         if(this%edge(i)%index(1) .eq. this%edge(i)%index(2))then
            if(present(indices))then
               if(all(this%edge(i)%index(1) .ne. indices)) cycle
            end if
            call this%remove_edges([i], update_adjacency=.false.)
         end if
      end do
      
      this%has_self_loops = .false.

  end subroutine remove_self_loops