The present invention relates to methods for expanding a stem cell population. The wedge and spool are threadedly coupled together to drive the wedge into and out of an opening in the assembly without hammering or prying. According to the iterated process, a point at a location of the global boundary is selected, a minimum rectangle with the given aspect ratio is grown from identified directions, and the largest rectangle encountered is delivered when the stopping condition has been met. An adaptive controller is coupled to the Volterra tap for modifying values in the lookup table. Such arrangements may be implemented, for example, using a Fabry-Perot resonator or a ring resonator in combination with a Mach-Zehnder interferometer or a Michelson interferometer.