code: def d_deta_from_phalf(arr, pfull_coord):
      
      d_deta = arr.diff(dim=internal_names.PHALF_STR, n=1)
      return replace_coord(d_deta, internal_names.PHALF_STR,
                           internal_names.PFULL_STR, pfull_coord)
docs: Compute pressure level thickness from half level pressures.