def _pdf(self, **kwargs):
        """Returns the pdf at the given values. The keyword arguments must
        contain all of parameters in self's params. Unrecognized arguments are
        ignored.
        """
        if kwargs not in self:
            return 0.
        return self._norm * \
            self._dfunc(numpy.array([kwargs[p] for p in self._params])).prod()
Returns the pdf at the given values. The keyword arguments must
        contain all of parameters in self's params. Unrecognized arguments are
        ignored.