Thank you for your answers. Following ur instruction, I checked again and found no mistakes. All of stocks have different returns. So "run time error 11: division by zero" is still not solved yet. As the result, I could not see any results. - Another question is that may i use this model to discover correlations between stocks? is it appeared in the covariance sheet? My portfolio consisted of 20 stocks, use daily returns, and 121 observations. Thank for ur helps.
