In this paper, we consider optimal portfolio selection when the covariance matrix of the asset returns is rank-deficient. For this case, the original Markowitz' problem does not have a unique solution. The possible solutions belong to either two subspaces namely the range- or nullspace of the...

Covariance matrix of the asset returns plays an important role in the portfolio selection. A number of papers is focused on the case when the covariance matrix is positive definite. In this paper, we consider portfolio selection with a singular covariance matrix. We describe an iterative method...

The random coeffcients model is an extension of the linear regression model which allows for additional heterogeneity in the population by modeling the regression coeffcients as random variables. Given data from this model, the statistical challenge is to recover information about the joint...

The random coeffcients model is an extension of the linear regression model which allows for additional heterogeneity in the population by modeling the regression coeffcients as random variables. Given data from this model, the statistical challenge is to recover information about the joint...