def spd(self, npos):
        '''raw spectral density, returns Fourier transform

        n is number of points in positive spectrum, the actual number of points
        is twice as large. different from other spd methods with fft
        '''
        n = npos
        w = fft.fftfreq(2*n) * 2 * np.pi
        hw = self.fftarma(2*n)  #not sure, need to check normalization
        #return (hw*hw.conj()).real[n//2-1:]  * 0.5 / np.pi #doesn't show in plot
        return (hw*hw.conj()).real * 0.5 / np.pi, w
dataset/ETHPy150Open statsmodels/statsmodels/statsmodels/sandbox/tsa/fftarma.py/ArmaFft.spd/original