pad1d Module Function

  module function pad1d(input, facets, pad_size, imethod) result(output)
    !! 1D padding operation
    implicit none

    ! Arguments
    type(array_type), intent(in), target :: input
    type(facets_type), intent(in) :: facets
    integer, intent(in) :: pad_size
    integer, intent(in) :: imethod
    type(array_type), pointer :: output

    ! Local variables
    integer :: i, m, s
    integer :: idx_in, idx_out
    integer :: input_size, output_size
    integer, dimension(3) :: output_shape

    input_size = input%shape(1)
    output_size = input_size +  2 * pad_size

    output_shape = [ output_size, input%shape(2), size(input%val, dim=2) ]
    output => input%create_result(array_shape = output_shape)

    ! save the facet values to indices and adj_ja
    allocate(output%indices(2 + facets%num))
    output%indices(1) = imethod
    output%indices(2) = pad_size
    output%indices(3) = facets%num
    allocate(output%adj_ja(2, 2 * facets%num))
    do i = 1, facets%num
       output%adj_ja(1,(i-1)*2 + 1) = facets%orig_bound(1,1,i)
       output%adj_ja(2,(i-1)*2 + 1) = facets%dest_bound(1,1,i)
       output%adj_ja(1,(i-1)*2 + 2) = facets%orig_bound(2,1,i)
       output%adj_ja(2,(i-1)*2 + 2) = facets%dest_bound(2,1,i)
    end do

    ! Initialise with pad_value
    output%val = 0._real32

    ! Copy input into the correct location in output
    do concurrent( &
         s = 1:output_shape(3), &
         m = 1:output_shape(2), &
         i = 1:input_size)
       idx_in = i + (m-1) * input_size
       idx_out = i + pad_size + (m-1) * output_size
       output%val(idx_out, s) = input%val(idx_in, s)
    end do

    if(output%indices(1) .ge. 3 .and. output%indices(1) .le. 5)then
       call fill_edge_region_1d( input, output )
    end if


    output%get_partial_left => get_partial_pad1d
    output%get_partial_left_val => get_partial_pad1d_val
    if(input%requires_grad)then
       output%requires_grad = .true.
       output%is_forward = input%is_forward
       output%operation = 'pad'
       output%left_operand => input
    end if

  end function pad1d