[R] xyplot help

I have a question about xyplot. Suppose I want to plot say a response variable y vs a predictor x within groups defined by a variable called z. And suppose I have another variable v=1,2 with two levels. I would use the following command to get a "spaghetti plot" with two panels defined by v. x

[R] difference between nlm and nlminb

Hi, I was wondering if someone could give a brief, big picture overview of the difference between the two optimization functions nlm and nlminb. I'm not familiar with PORT routines, so I was hoping someone could give an explanation. Thanks, Angelo __