clear Module Subroutine

  module subroutine clear(this)
    !! Clear all data from the graph.
    !!
    !! This deallocates all arrays and resets all variables to their default values.
    implicit none

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

    ! Deallocate all allocatable arrays
    if(allocated(this%graph_features)) deallocate(this%graph_features)
    if(allocated(this%name)) deallocate(this%name)
    if(allocated(this%adjacency)) deallocate(this%adjacency)
    if(allocated(this%adj_ia)) deallocate(this%adj_ia)
    if(allocated(this%adj_ja)) deallocate(this%adj_ja)
    if(allocated(this%edge_weights)) deallocate(this%edge_weights)
    if(allocated(this%vertex_features)) deallocate(this%vertex_features)
    if(allocated(this%edge_features)) deallocate(this%edge_features)
    if(allocated(this%vertex)) deallocate(this%vertex)
    if(allocated(this%edge)) deallocate(this%edge)

    ! Reset all scalar variables to default values
    this%directed = .false.
    this%is_sparse = .false.
    this%has_self_loops = .false.
    this%num_vertices = 0
    this%num_edges = 0
    this%num_vertex_features = 0
    this%num_edge_features = 0
    this%num_graph_features = 0
  end subroutine clear