code: def get_rlzs_by_gsim(oqparam):
      
      cinfo = source.CompositionInfo.fake(get_gsim_lt(oqparam))
      ra = cinfo.get_rlzs_assoc()
      dic = {}
      for rlzi, gsim_by_trt in enumerate(ra.gsim_by_trt):
          dic[gsim_by_trt['*']] = [rlzi]
      return dic
docs: Return an ordered dictionary gsim -> [realization index]. Work for
      gsim logic trees with a single tectonic region type.