def pdf(self, phi):
if self._n is None:<EOL><INDENT>pdf = np.empty_like(phi)<EOL>pdf.fill(<NUM_LIT>/np.pi)<EOL>return pdf<EOL><DEDENT>phi = np.asarray(phi)<EOL>pdf = self._pdf(phi)<EOL>pdf /= <NUM_LIT>*np.pi<EOL>return pdf<EOL>
r"""
        Evaluate the flow PDF `dN/d\phi`.

        :param array-like phi: Azimuthal angles.

        :returns: The flow PDF evaluated at ``phi``.