  In these notes we discuss investment allocation to multiple alpha streams
traded on the same execution platform, including when trades are crossed
internally resulting in turnover reduction. We discuss approaches to alpha
weight optimization where one maximizes P&L subject to bounds on volatility (or
Sharpe ratio). The presence of negative alpha weights, which are allowed when
alpha streams are traded on the same execution platform, complicates the
optimization problem. By using factor model approach to alpha covariance
matrix, the original optimization problem can be viewed as a 1-dimensional root
searching problem plus an optimization problem that requires a finite number of
iterations. We discuss this approach without costs and with linear costs, and
also with nonlinear costs in a certain approximation, which makes the
allocation problem tractable without forgoing nonlinear portfolio capacity
bound effects.
