Andrew, We should have included a reference (which I'll make below), we went over reparameterization in secton on thursday. The basic idea is that optim looks over the whole real number line to find a value that maximizes a function, but there are often instances where we need to constrain the search. For example, when we want to find the maximum likelihood estimate of a probability, we only want optim to search between 0 and 1. Reparameterization (using some function) allows us to constrain the search without resorting to constrained optimization routines, which tend to perform much more slowly than optim. The video from section has been posted on the website, and we've included an example of reperameterization in the section notes on the class website. Note, that this example is for constrained search over the positive part of the real line. Cheers, Justin On Sat, 3 Mar 2007, Andrew Coe wrote: