[R] Bounding or constraining parameters in non-linear regressions

[mwdavis@nist.gov]

Dear R-Users,

Being an engineer and not a statistician, my desired course of action may 
either be impossible or very simple.

I am attempting to fit a non-linear model to some measured data.  One term in 
the model contains a square-root, but in the course of regression, this term 
turns negative and an error occurs.  I started using Micrsoft's Excel Solver, 
and then I turned to NIST's Datplot statistical package.  I can constrain in 
Solver, but it violates those constraints. :)  Dataplot does not have the 
capability to constrain parameters.

Does R have the capability to constrain or bound parameters in non-linear 
regressions?


Thanks,
Mark Davis