1. An apparatus, comprising: a simulator configured to simulate a system and to propagate at least one first state of the simulated system through time in response to a value of a first parameter; a generator configured to generate a representation of a region of a first plot having dimensions that respectively correspond at least to the parameter and to a characteristic of a second state of the simulated system, and a representation of a region of a second plot having dimensions that respectively correspond at least to the parameter and to a characteristic of a third state of the simulated system; and a determiner configured to determine a next value of the parameter in response to the representations of the regions of the first and second plots.