Free all the resources used by an lpSolve linear program model object and set the value of the external pointer to NULL.
NULL
delete.lp(lprec)
an lpSolve linear program model object.
lprec is invisibly returned.
lprec
This function is used as a finalizer for lpSolve linear program model objects.
http://lpsolve.sourceforge.net/5.5/index.htm