madness object. Note that the value and the
derivative cannot easily be changed, as allowing this form of access would
likely result in badly computed derivatives.xtag(x) <- value# S4 method for madness
xtag(x) <- value
vtag(x) <- value
# S4 method for madness
vtag(x) <- value
varx(x) <- value
# S4 method for madness
varx(x) <- value
madness object.