the DTI model section has been coded.  I need to double check my 2nd derivatives, and it may also be easier to forget the logging of the diagonals and just use them as reals.  My main issue right now, I think, is that I don't have a good starting point.  I'm also never completely sure whether or not my simulations even SHOULD give a reasonable result.  I should code the cramer rao lower bound for the variance, and then look at that before running a simulation, just so I know if I should even reasonably expect it to work.  I also should consider running a linear reg on the q components to find a starting model.