kipf_propagate Module Function

  module function kipf_propagate(vertex_features, adj_ia, adj_ja) result(c)
    !! Propagate values from one autodiff array to another
    implicit none

    ! Arguments
    class(array_type), intent(in), target :: vertex_features
    !! Vertex feature tensor
    integer, dimension(:), intent(in) :: adj_ia
    !! CSR row pointers
    integer, dimension(:,:), intent(in) :: adj_ja
    !! CSR neighbour and edge lookup indices
    type(array_type), pointer :: c
    !! Propagated node feature tensor

    ! Local variables
    integer :: v, w
    !! Vertex and adjacency traversal indices
    real(real32) :: coeff
    !! Symmetric normalisation coefficient per edge

    c => vertex_features%create_result()
    ! propagate 1D array by using shape to swap dimensions
    do concurrent(v = 1:size(vertex_features%val,2))
       c%val(:,v) = 0._real32
       do w = adj_ia(v), adj_ia(v+1)-1

          ! if( adj_ja(2,w) .eq. 0 )then
          !    coeff = 1._real32
          ! !else
          ! !   coeff = edge_weights(adj_ja(2,w))
          ! end if
          !coeff = coeff * ( &
          coeff = ( &
               ( adj_ia(v+1) - adj_ia(v) ) * &
               ( adj_ia( adj_ja(1,w) + 1 ) - adj_ia( adj_ja(1,w) ) ) &
          ) ** ( -0.5_real32 )

          c%val(:,v) = c%val(:,v) + coeff * [ vertex_features%val(:, adj_ja(1, w)) ]
       end do
    end do

    c%indices = adj_ia
    c%adj_ja = adj_ja
    c%get_partial_left => get_partial_kipf_propagate_left
    c%get_partial_left_val => get_partial_kipf_propagate_left_val
    if(vertex_features%requires_grad)then
       c%requires_grad = .true.
       c%is_forward = vertex_features%is_forward
       c%operation = 'kipf_propagate'
       c%left_operand => vertex_features
       c%owns_left_operand = vertex_features%is_temporary
    end if
  end function kipf_propagate