1. A simulation method allowing an information processing unit to perform calculation, the calculation comprising: decomposing each of a plurality of incident fluxes into flux components in respective unit vector directions that are orthogonal to each other, the plurality of incident fluxes entering, at an arbitrary position, a surface of a processing target that is a target of a predetermined processing; summing up the flux components for each of the plurality of unit vector directions; and synthesizing a plurality of flux components into one vector, the plurality of flux components being summations in the respective unit vector directions and being orthogonal to each other, and thereby calculating a normal vector at the arbitrary position on the surface of the processing target.