def fit(self, y, exogenous=None):
        """Fit the transformer

        Computes the periods of all the Fourier terms. The values of ``y`` are
        not actually used; only the periodicity is used when computing Fourier
        terms.

        Parameters
        ----------
        y : array-like or None, shape=(n_samples,)
            The endogenous (time-series) array.

        exogenous : array-like or None, shape=(n_samples, n_features), optional
            The exogenous array of additional covariates. If specified, the
            Fourier terms will be column-bound on the right side of the matrix.
            Otherwise, the Fourier terms will be returned as the new exogenous
            array.
        """
        # Since we don't fit any params here, we can just check the params
        _, _ = self._check_y_exog(y, exogenous, null_allowed=True)

        m = self.m
        k = self.k
        if k is None:
            k = m // 2
        if 2 * k > m or k < 1:
            raise ValueError("k must be a positive integer not greater "
                             "than m//2")

        # Compute the periods of all Fourier terms. Since R allows multiple
        # seasonality and we do not, we can do this much more simply.
        p = ((np.arange(k) + 1) / m).astype(np.float64)  # 1:K / m

        # If sinpi is 0... maybe blow up?
        # if abs(2 * p - round(2 * p)) < np.finfo(y.dtype).eps:  # min eps

        self.p_ = p
        self.k_ = k
        self.n_ = y.shape[0]

        return self
Fit the transformer

        Computes the periods of all the Fourier terms. The values of ``y`` are
        not actually used; only the periodicity is used when computing Fourier
        terms.

        Parameters
        ----------
        y : array-like or None, shape=(n_samples,)
            The endogenous (time-series) array.

        exogenous : array-like or None, shape=(n_samples, n_features), optional
            The exogenous array of additional covariates. If specified, the
            Fourier terms will be column-bound on the right side of the matrix.
            Otherwise, the Fourier terms will be returned as the new exogenous
            array.