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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 evaluate_wavefunc(self, kpoint, band, r, spin=0):
 r""" Evaluates the wavefunction for a given position, r. The wavefunction is given by the k-point and band. It is evaluated at the given position by summing over the components. Formally, \psi_n^k (r) = \sum_{i=1}^N c_i^{n,k} \exp (i (k + G_i^{n,k}) \cdot r) where \psi_n^k is the wavefunction for the nth band at k-point k, N is the number of plane waves, c_i^{n,k} is the ith coefficient that corresponds to the nth band and k-point k, and G_i^{n,k} is the ith G-point corresponding to k-point k. NOTE: This function is very slow; a discrete fourier transform is the preferred method of evaluation (see Wavecar.fft_mesh). Args: kpoint (int):
 the index of the kpoint where the wavefunction will be evaluated band (int):
 the index of the band where the wavefunction will be evaluated r (np.array):
 the position where the wavefunction will be evaluated spin (int):
 spin index for the desired wavefunction (only for ISPIN = 2, default = 0) Returns: a complex value corresponding to the evaluation of the wavefunction """

        v = self.Gpoints[kpoint] + self.kpoints[kpoint]
        u = np.dot(np.dot(v, self.b), r)
        c = self.coeffs[spin][kpoint][band] if self.spin == 2 else \
            self.coeffs[kpoint][band]
        return np.sum(np.dot(c, np.exp(1j * u, dtype=np.complex64))) / \
               np.sqrt(self.vol)