use optim() for finding optimal value of switchpoint

[Aariq]

optim() requires a function with the parameter to be optimized as the first argument that returns some kind of score like log-likelihood. Consider using optim() inside of brkpt() instead of iterating over meshpoints of tau to find value of tau that maximizes likelihood.

A new, lowest level function could be created that only takes a formula like size ~ time and a value for the switchpoint, tau, and fits the modified lm (with .post in the formula). Then, if brkpt() is called with no value of tau supplied, it uses optim() to optimize tau, then re-fits model with that new function. If brkpt() is called with a value of tau, then it skips the optimization step.

related:

• bumbl submission ropenscilabs/statistical-software-review#2 (comment)
• allow user to supply vector of tau, one value per colony #55
• Warning when number of time steps >> number of tau values #51

[Aariq]

optimize() is the single parameter version