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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def levenberg_marquardt(self, start_x=None, damping=1.0e-3, tolerance=1.0e-6):
 """ Optimise value of x using levenberg marquardt """

        if start_x is None:
            start_x = self._analytical_fitter.fit(self._c)
        return optimise_levenberg_marquardt(start_x, self._a, self._c, tolerance)