code: def _pdf(self, **kwargs):
          
          if kwargs in self:
              vals = numpy.array([numpy.log(10) * self._norm * kwargs[param]
                                  for param in kwargs.keys()])
              return 1.0 / numpy.prod(vals)
          else:
              return 0.
docs: Returns the pdf at the given values. The keyword arguments must
          contain all of parameters in self's params. Unrecognized arguments are
          ignored.