nlm optimization in the lme
function. If all initial values are zero, the scale is set to one for
all coefficients; else, the scale for a coefficient with non-zero
initial value is equal to the inverse of its initial value and the
scale for the coefficients with initial value equal to zero is set to
the median of the non-zero initial value coefficients.lmeScale(start)nlm for estimating the
coefficients.nlm