def polyfit(self, sampled):
        """
        Compute Chebyshev coefficients for values located on Chebyshev points.
        sampled: array; first dimension is number of Chebyshev points
        """
        asampled = np.asarray(sampled)
        if len(asampled) == 1:
            return asampled
        evened = even_data(asampled)
        coeffs = dct(evened)
        return coeffs