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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def A(self):
 """Spectral VAR coefficients. .. math:: \mathbf{A}(f) = \mathbf{I} - \sum_{k=1}^{p} \mathbf{a}^{(k)} \mathrm{e}^{-2\pi f} """

        return fft(np.dstack([np.eye(self.m), -self.b]),
                   self.nfft * 2 - 1)[:, :, :self.nfft]