an optional character string with a description of
the varFunc
class. Default depends on the method function:
"Combination of variance functions"
for varComb
,
"Constant plus power of covariate"
for varConstPower
,
"Exponential of variance covariate"
for varExp
,
"Different standard deviations per stratum"
for varIdent
,
"Power of variance covariate"
for varPower
, and
data.class(object)
for varFunc
.