eventually would be good to make it possible to pass any inputs for local optimization, in a way that doesn't make code messy. eg.abs_tol, rel_tol from Optim or the maximum time thing from NLopt
"a while ago we deleted number of iterations and another measure of convergence. should we bring back one of them?"
=> no, NLopt doesn't support those things
"should we put setup inside the saved results?"
=> no, unnecessary extra work
"make it possible to pass any inputs for local optimization"
=> taking care of it
Some ideas: