@classmethod<EOL><INDENT>def identity(cls, domain=None, window=None):<DEDENT>
if domain is None:<EOL><INDENT>domain = cls.domain<EOL><DEDENT>if window is None:<EOL><INDENT>window = cls.window<EOL><DEDENT>off, scl = pu.mapparms(window, domain)<EOL>coef = cls._line(off, scl)<EOL>return cls(coef, domain, window)<EOL>
Identity function.

        If ``p`` is the returned series, then ``p(x) == x`` for all
        values of x.

        Parameters
        ----------
        domain : {None, array_like}, optional
            If given, the array must be of the form ``[beg, end]``, where
            ``beg`` and ``end`` are the endpoints of the domain. If None is
            given then the class domain is used. The default is None.
        window : {None, array_like}, optional
            If given, the resulting array must be if the form
            ``[beg, end]``, where ``beg`` and ``end`` are the endpoints of
            the window. If None is given then the class window is used. The
            default is None.

        Returns
        -------
        new_series : series
             Series of representing the identity.