Class "unpackedMatrix" is the virtual class of dense
matrices in "unpacked" format, storing all m*n elements of
an m-by-n matrix. It is used to define common methods
for efficient subsetting, transposing, etc. of its proper
subclasses: currently "[dln]geMatrix" (unpacked general),
"[dln]syMatrix" (unpacked symmetric), "[dln]trMatrix"
(unpacked triangular), and subclasses of these, such as
"dpoMatrix",
"Cholesky", and
"BunchKaufman".