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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 _eta_from_phi(self):
 """Update `eta` using current `phi`."""

        self.eta = scipy.ndarray(N_NT - 1, dtype='float')
        etaprod = 1.0
        for w in range(N_NT - 1):
            self.eta[w] = 1.0 - self.phi[w] / etaprod
            etaprod *= self.eta[w]
        _checkParam('eta', self.eta, self.PARAMLIMITS, self.PARAMTYPES)