@staticmethod
def fit_deriv(x, amplitude, x_0, fwhm):
    """One dimensional Lorentzian model derivative with respect to parameters"""
    d_amplitude = fwhm ** 2 / (fwhm ** 2 + (x - x_0) ** 2)
    d_x_0 = amplitude * d_amplitude * (2 * x - 2 * x_0) / (fwhm ** 2 + (x -
        x_0) ** 2)
    d_fwhm = 2 * amplitude * d_amplitude / fwhm * (1 - d_amplitude)
    return [d_amplitude, d_x_0, d_fwhm]
