compute +DM and -DM

[wellzero]

found many reference compute +-DM like following

    dm_pos = pd.DataFrame(np.where(high_chg > **0**, high_chg, 0), index=self.df.index, columns=['dm_pos'])
    dm_neg = pd.DataFrame(np.where(low_chg > **0**, low_chg, 0), index=self.df.index, columns=['dm_neg'])        

following is our repo code, want to know why is different with upper

compute +DM and -DM

    dm_pos = pd.DataFrame(np.where(high_chg > **low_chg**, high_chg, 0), index=self.df.index, columns=['dm_pos'])
    dm_neg = pd.DataFrame(np.where(low_chg > **high_chg**, low_chg, 0), index=self.df.index, columns=['dm_neg'])