code: def qhalfx(self):
          
          if self.__qhalfx is None:
              self.log("qhalfx")
              self.__qhalfx = self.qhalf * self.jco
              self.log("qhalfx")
          return self.__qhalfx
docs: get the half normal matrix attribute.  Create the attribute if
          it has not yet been created
  
          Returns
          -------
          qhalfx : pyemu.Matrix