[R] psi not functioning in nlrob?

[Xiao Xiao]

Hi all,

I'm trying to fit a nonlinear regression by "nlrob":

 model3=nlrob(y~a1*x^a2,data=transient,psi=psi.bisquare,
start=list(a1=0.02,a2=0.7),maxit=1000)

However an error message keeps popping up saying that the function
psi.bisquare doesn't exist.

I also tried psi.huber, which is supposed to be the default for nlrob:

model3=nlrob(y~a1*x^a2,data=transient,psi=psi.huber,
start=list(a1=0.02,a2=0.7),maxit=1000)

But I still got the same error message - psi.huber doesn't exist.

Is the argument "psi" not available in nlrob?

Any help will be appreciated.

Best,
Xiao Xiao