public abstract class CallbackFunction
A callback function (along the lines of Berkeley optimization repo), which is currently used in the optimization package.
In the optimization package, it is used for passing values (newX, iteration, newObjectiveValue, newGradient) at every iteration and
then you can do whatever you want with those values.
One use case is to print the values in a file; another is do some sanity check etc.
Created by sonalg on 2/4/15.