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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 dr( self, cell_lengths ):
 """ Particle displacement vector for this jump Args: cell_lengths (np.array(x,y,z)):
 Cell lengths for the orthogonal simulation cell. Returns (np.array(x,y,z)):
 dr """

        half_cell_lengths = cell_lengths / 2.0
        this_dr = self.final_site.r - self.initial_site.r
        for i in range( 3 ):
            if this_dr[ i ] > half_cell_lengths[ i ]:
                this_dr[ i ] -= cell_lengths[ i ]
            if this_dr[ i ] < -half_cell_lengths[ i ]:
                this_dr[ i ] += cell_lengths[ i ]
        return this_dr