index_array Module Function

  module function index_array(a, indices) result(c)
    !! Index an autodiff array
    implicit none
    class(array_type), intent(in), target :: a
    integer, dimension(:), intent(in) :: indices
    type(array_type), pointer :: c

    integer :: i, s

    allocate(c)
    call c%allocate(array_shape=[size(a%val,1), size(indices)])
    do concurrent(s=1:size(indices), i=1:size(a%val,1))
       c%val(i, s) = a%val(i, indices(s))
    end do
    c%indices = indices

    c%get_partial_left => get_partial_index
    if(a%requires_grad) then
       c%requires_grad = .true.
       c%is_forward = a%is_forward
       c%operation = 'index'
       c%left_operand => a
       c%owns_left_operand = a%is_temporary
    end if
  end function index_array