def _to_array(self, alpha, normalization='4pi', csphase=1):
        """
        Return the spherical harmonic coefficients of Slepian function i as an
        array, where i=0 is the best concentrated function.
        """
        coeffs = _shtools.SHVectorToCilm(self.tapers[:, alpha])

        if normalization == 'schmidt':
            for l in range(self.lmax + 1):
                coeffs[:, l, :l+1] *= _np.sqrt(2.0 * l + 1.0)
        elif normalization == 'ortho':
            coeffs *= _np.sqrt(4.0 * _np.pi)

        if csphase == -1:
            for m in range(self.lmax + 1):
                if m % 2 == 1:
                    coeffs[:, :, m] = - coeffs[:, :, m]

        return coeffs
Return the spherical harmonic coefficients of Slepian function i as an
        array, where i=0 is the best concentrated function.