projectionplotvariables: Projection Plot Variables
In ruv: Detect and Remove Unwanted Variation using Negative Controls

Calculates the variables necessary to produce a projection plot.

1	projectionplotvariables(Y, X, W)

`Y`	The data. A m by n matrix, where m is the number of samples and n is the number of features.
`X`	A m by p matrix containing the factor(s) of interest.
`W`	A m by k matrix containing the estimated unwanted factors.

Typically intended for internal use, and called after adjustment for known covariates (Z).

A list containing

`byx`	Regression coefficients from regressing Y on X.
`bwx`	Regression coefficients from regressing W on X.
`projectionplotalpha`	A reparameterization of alpha.
`projectionplotW`	A reparameterization of W.