1. A method of synthesizing a photolithographic data set, comprising: using a first computational model to calculate a first figure-of-merit of the photolithographic data set; changing a first part of the photolithographic data set to increase said first figure-of-merit; using a second computational model to calculate a second figure-of-merit of the photolithographic data set, wherein the second computational model executes faster than said first computational model; and changing a second part of the photolithographic data set to increase the second figure-of-merit.