A matrix, usually including one or more NA entries,
coerced to integer (a board); see details section
Details
Function marginals() takes a matrix and returns a list holding
the marginal totals and the coordinates of blank squares.
Function dof() takes a board and returns the number of degrees
of freedom present.
Function .Cargs() takes a matrix and coerces it to a list
suitable for calling the C++ routines; it is not really
intended for the end-user. This function uses formal S4 methods to
coerce a matrix to an object of class board (checking for
non-integer entries, etc), as do the functions documented in
allboards.Rd.