1. A non-transitory tangible computer-readable medium storing a program for making a computer execute a process of calculating a light intensity distribution formed on an image plane of a projection optical system upon illuminating a mask using an illumination optical system and projecting an image of a pattern of the mask onto a substrate via the projection optical system, the program making the computer execute: a division step of dividing an effective light source formed on a pupil plane of the projection optical system into a plurality of point sources; a generation step of shifting a pupil function describing a pupil of the projection optical system for each of the plurality of point sources in accordance with positions thereof, thereby generating a plurality of shifted pupil functions; a defining step of defining a matrix by arranging each of the plurality of pupil functions generated in the generation step in each row or each column of the matrix; a first calculation step of performing singular value decomposition of the matrix defined in the defining step, thereby calculating an eigenvalue and an eigenfunction; and a second calculation step of calculating the light intensity distribution formed on the image plane of the projection optical system, based on a distribution of the light diffracted by the pattern of the mask, and the eigenvalue and the eigenfunction calculated in the first calculation step.