covar provides a mechanism for creating formula
objects that specify such linearizations.covar(x,...,scope=<>, method=<>) locus allows.x evaluates to a single value, then additional
atomic elements may be included as with locus.covar actually only returns x. The real
work is done by a covar function that is hidden inside of
bqtl, where the arguments are parsed as for locus. Each
of the return values from locus is prefixed by "covar(" and
suffixed by ")". If x is a name of a locus or effect, then
paste("covar(",deparse(x),")") is returned. Later, when
bqtl calls lapadj, terms like covar(PVV4.1) are
recognized as requiring a linearization w.r.t. effect 'PVV4.1'.locus, add, dom,
configs