1. A method, comprising: determining information for an object to be simulated for a photolithographic manufacturing process using a sum of coherent systems (SOCS) approximation; determining a set of kernels for use in the SOCS approximation, wherein one or more of the kernels in the set are associated with importance values, and wherein the set of kernels are in a first order based on the importance values; using a computer, analyzing the set of kernels and the information for the object to determine a different importance value for one or more of the kernels in the set of kernels; and assigning a different importance value for one or more kernels in the set of kernels based on the analysis.