sum_array Module Function

  module function sum_array(a, dim) result(c)
    !! Sum values along a dimension - optimized version
    implicit none
    class(array_type), intent(in), target :: a
    integer, intent(in) :: dim
    type(array_type), pointer :: c

    integer :: s, i, n_rows, n_cols

    ! Cache dimensions
    n_rows = size(a%val, 1)
    n_cols = size(a%val, 2)

    if(dim.eq.1)then
       c => a%create_result(array_shape=[1, n_cols])
       c%val(1,:) = sum(a%val, dim=1)
    else if(dim.eq.2)then
       c => a%create_result(array_shape=[a%shape, 1])
       c%val(:,1) = sum(a%val, dim=2)
       c%is_sample_dependent = .false.
    else
       call stop_program("sum_array: only 1 or 2 dimensions are supported")
    end if
    c%indices = [dim, 1]

    c%get_partial_left => get_partial_sum
    !c%get_partial_right => get_partial_sum_forward
    c%get_partial_left_val => get_partial_sum_val
    c%get_partial_left_val_sum => get_partial_sum_val_sum
    if(a%requires_grad)then
       c%requires_grad = .true.
       c%is_forward = a%is_forward
       c%operation = 'sum_array'
       c%left_operand => a
       c%owns_left_operand = a%is_temporary
    end if

  end function sum_array