df.loc[i, 'Pred'] = df.loc[prev, 'Pred'](1 + df.loc[i, 'Pred_ret'])
why donot use the true price of two days ago but use predict price to predict the current price;
i think use this maybe more realisticdf.loc[i, 'Pred'] = df.loc[prev, 'Gold'](1 + df.loc[i, 'Pred_ret']),because usually we will not predict such a long time ,so the real price of two days ago i think we can get