Expand a Decomposition into Factors --- Generic Function
DESCRIPTION:
Expands decompositions stored in compact form into factors.

This function is generic (see Methods); method functions can be written to handle specific classes of data. Classes which already have methods for this function include: "lu.Matrix", "lu.Hermitian", "qr.Matrix", "eigen.Matrix".

USAGE: 
expand(x, ...)
REQUIRED ARGUMENTS:
x:
a matrix decomposition.
OPTIONAL ARGUMENTS:
...:
the method for "qr.Matrix" has an additional argument.
VALUE:
the expanded decomposition.
NOTE:
Factors for decompositions such as lu and qr can be stored in a compact form. The function expand allows all factors to be fully expanded.
REFERENCES:
Golub, G., and Van Loan, C. F. (1989). Matrix Computations, 2nd edition, Johns Hopkins, Baltimore.
SEE ALSO:
expand.lu.Matrix , expand.lu.Hermitian , expand.qr.Matrix , expand.eigen.Matrix , facmul .
EXAMPLES: 
library(Matrix)
x <- Matrix( 1:9, 3, 3)
expand(qr(x))