Is it inadvisable (or advised) to use the Jacobian matrix of residual variance-covariance matrix (that is singular) in the context of SUR estimations?

Good evening everybody. I want to run Seemingly Unrelated Regressions (SUR) but the Variance-covariance matrix obtained is singular. But, in my estimations, I found that when I replaced the...

04 January 2016 5,467 3 View