More updates and downside risk measures

Another update the the paper is coming out. Michele Costola caught me playing a little fast and loose with π and E(r) in the paper. Somebody else had already noticed this in the cookbook webpage, but now I'm also fixing up the paper. Probably most people won't notice much, but the symbols will now be more consistent throughout the paper.

I read an interesting paper, "The Black-Litterman Model for Active Portfolio Management" by Da Silva, Lee and Pornrojnangkool. The thrust of their argument is that it isn't always right to consider the prior portfolio as being the mean-variance efficient portfolio from CAPM. If one is using Black-Litterman for active management then one should be considering information ratio. I'd like to add this paper to the literature survey paper in some upcoming round.