'One dimensional Sine model derivative'

@staticmethod
def fit_deriv(x, amplitude, frequency, phase):

    d_amplitude = np.sin((((TWOPI * frequency) * x) + (TWOPI * phase)))
    d_frequency = (((TWOPI * x) * amplitude) * np.cos((((TWOPI * frequency) * x) + (TWOPI * phase))))
    d_phase = ((TWOPI * amplitude) * np.cos((((TWOPI * frequency) * x) + (TWOPI * phase))))
    return [d_amplitude, d_frequency, d_phase]
