same than for a Brownian motion model.
}
\value{
an object of class \code{"corPagel"}, the coefficients from an object
of this class, or the correlation matrix of an initialized object of
same than for a Brownian motion model.
}
\value{
an object of class \code{"corPagel"}, the coefficients from an object
of this class, or the correlation matrix of an initialized object of