'Gaussian1D model function derivatives.'

@staticmethod
def fit_deriv(x, amplitude, mean, stddev):

    d_amplitude = np.exp((((-0.5) / (stddev ** 2)) * ((x - mean) ** 2)))
    d_mean = (((amplitude * d_amplitude) * (x - mean)) / (stddev ** 2))
    d_stddev = (((amplitude * d_amplitude) * ((x - mean) ** 2)) / (stddev ** 3))
    return [d_amplitude, d_mean, d_stddev]
