rms.curv {MASS}  R Documentation 
Calculates the root mean square parameter effects and intrinsic relative curvatures, c^theta and c^iota, for a fitted nonlinear regression, as defined in Bates & Watts, section 7.3, p. 253 et seq.
rms.curv(obj)
obj 
Fitted model object of class "nls" . The model must be fitted using the
default algorithm.

The method of section 7.3.1 of Bates & Watts is implemented. The
function deriv3
should be used generate a model function with first
derivative (gradient) matrix and second derivative (Hessian) array
attributes. This function should then be used to fit the nonlinear
regression model.
A print method, print.rms.curv
, prints the pc
and
ic
components only, suitably annotated.
If either pc
or ic
exceeds some threshold (0.3 has been
suggested) the curvature is unacceptably high for the planar assumption.
A list of class rms.curv
with components pc
and ic
for parameter effects and intrinsic relative curvatures multiplied by
sqrt(F), ct
and ci
for c^theta and c^iota (unmultiplied),
and C
the Carray as used in section 7.3.1 of Bates & Watts.
Bates, D. M, and Watts, D. G. (1988) Nonlinear Regression Analysis and its Applications. Wiley, New York.
# The treated sample from the Puromycin data data(Puromycin) mmcurve < deriv3(~ Vm * conc/(K + conc), c("Vm", "K"), function(Vm, K, conc) NULL) Treated < Puromycin[Puromycin$state == "treated", ] (Purfit1 < nls(rate ~ mmcurve(Vm, K, conc), data = Treated, start = list(Vm=200, K=0.1))) rms.curv(Purfit1) ##Parameter effects: c^theta x sqrt(F) = 0.2121 ## Intrinsic: c^iota x sqrt(F) = 0.092