calculate_degree Module Subroutine

  module subroutine calculate_degree(this)
    !! Calculate the degree of the vertices in the graph.
    implicit none

    ! Arguments
    class(graph_type), intent(inout) :: this
    !! Parent. Instance of the graph structure.

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

    ! Calculate vertex degrees based on storage format
    if(.not. this%is_sparse)then
       ! Dense graph: count non-zero adjacency entries
       this%vertex(:)%degree = 0
       do i = 1, this%num_vertices
          do j = 1, this%num_vertices
             if(this%adjacency(i,j) .gt. 0)then
                this%vertex(i)%degree = this%vertex(i)%degree + 1
             end if
          end do
       end do
    elseif(this%is_sparse .and. .not. this%directed)then
       ! Sparse undirected graph: use CSR row pointers
       this%vertex(:)%degree = 0
       do i = 1, this%num_vertices
          this%vertex(i)%degree = this%adj_ia(i+1) - this%adj_ia(i)
       end do
    else
       ! Sparse directed graph not yet implemented
       call stop_program('Degree calculation for sparse directed graphs not implemented')
    end if

  end subroutine calculate_degree