Selecting the optimal portfolio is one of the important issues in the investment field. The optimization techniques presented in financial theories can help investors better select portfolio. Markovitz's mean-variance model is one of the first methods introduced in this field. There are some flaws in the practical use of the Markowitz model, including an error in estimating model inputs. Due to the problems in this model and in order to provide an efficient model to cover the disadvantages of the previous models, a model for the allocation of assets by Black and Letterman was introduced.
