Additional methods for QRdecomposition class

[Douglas Bates <bates@stat.wisc.edu>]

May I suggest that more methods be added to the QRdecomposition class?
In particular, I would suggest
 public Matrix QMultiply (Matrix B)
that forms QB from B and
 public Matrix QTransMultiply (Matrix B)
that forms transpose(Q)B from B.

It may even be worthwhile having methods such as
 public Matrix QMultiplyEquals (Matrix B)
and
 public Matrix QTransMultiplyEquals (Matrix B)
to provide in-place versions of these operations.

Other possibilities are methods to project the columns of a Matrix B
onto the column space of the original matrix X or onto its orthogonal
complement.  These are very useful in statistical computing.  Back in
the days of Linpack these operations were available through dqrsl.