code: def _logpdf(self, **kwargs):
          
          for p in self._params:
              if p not in kwargs.keys():
                  raise ValueError(
                              'Missing parameter {} to construct pdf.'.format(p))
          if kwargs in self:
              log_pdf = self._lognorm + \
                        (self.dim - 1) * \
                        numpy.log([kwargs[p] for p in self._params]).sum()
              return log_pdf
          else:
              return -numpy.inf
docs: Returns the log of the pdf at the given values. The keyword
          arguments must contain all of parameters in self's params. Unrecognized
          arguments are ignored.