You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: get_geopot_normal_trunc.m
    path of file: ./repos/mpsim/lib/geod
    
    the code of the file until where you have to start completion: function U = get_geopot_normal_trunc (pos_sph, ell)
%GET_GEOPOT_NORMAL_TRUNC: Return the normal geopotential (single-term truncated series), given a position in global spherical -- NOT GEODETIC -- coordinates.


    
function U = get_geopot_normal_trunc (pos_sph, ell)
%GET_GEOPOT_NORMAL_TRUNC: Return the normal geopotential (single-term truncated series), given a position in global spherical -- NOT GEODETIC -- coordinates.

% Compute the normal gravity potential by means of
% an expansion of that potential in spherical coordinates,
% TRUNCATED at degree 1 (n = 1). The error is approximately
% 350 m^2/s^2 (or 35 m, for the corresponding height) 
% on the ellipsoid.
%
% Use instead get_geopot_normal().
    if isempty(pos_sph),  U = zeros(0,1);  return;  end