ReducedRankRegressions: Construct a poset of reduced rank regression models.
Description
Creates an object representing a collection of reduced rank regression
models. There is one model for each fixed rank from 1 to some specified
maximum. In particular each model is identified by a single number
specifiying the rank of the regression matrix in the model. Models are
naturally ordered by inclusion so that, for example, a model with 2
rank 2 comes before before a model with rank 3 or greater.