The height related to the Earth's 37 gravity field usually refers to the orthometric or normal height, which is strictly based on 38 the geopotential number CP ( 0 LVD P P C W W   , where 0 LVD W is the geopotential value for 39 the local vertical datum, and WP indicates the gravity potential for point P).
Line 259 refers to a x as a ’parameter’ in Eq 12, I suggest to use ’vector’ or ’parameter vector’ instead.