Constant Plus Power Variance Function
This function is a constructor for the varConstPower
class,
representing a constant plus power variance function
structure. Letting v denote the variance covariate and
s2(v) denote the variance function evaluated at
v, the constant plus power variance function is defined as
s2(v) = (t1 +
|v|^t2)^2, where t1, t2 are the variance
function coefficients. When a grouping factor is present, different
t1, t2 are used for each factor level.
varConstPower(const, power, form, fixed)
const, power |
optional numeric vectors, or lists of numeric
values, with, respectively, the coefficients for the constant
and the power terms. Both arguments must have length one, unless a
grouping factor is specified in |
form |
an optional one-sided formula of the form |
fixed |
an optional list with components |
a varConstPower
object representing a constant plus power
variance function structure, also inheriting from class
varFunc
.
José Pinheiro and Douglas Bates bates@stat.wisc.edu
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer.
vf1 <- varConstPower(1.2, 0.2, form = ~age|Sex)
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