1. A method implemented by a computer for reducing optical proximity effect in a design layout to be included in a mask used in a lithographic process, the method comprising: dividing patterns within the design layout into edge segments; identifying a plurality of neighboring edge segments that interact with each other due to the optical proximity effect; and computing, by using a computer, an amount of movement of each of the identified neighboring edge segments for reducing the optical proximity effect, the computing including maintaining a plurality of model values that can be used to predict a change in an image value associated with each of the identified neighboring edge segments given a correction amount of movement wherein the optimal amount of movement is computed for the identified neighboring edge segments in terms of alteration of image values at predefined locations in the design layout; wherein the plurality of model values are arranged in a matrix form, the matrix being used to compute the amount of movement; and wherein the matrix comprises a sparse matrix, where matrix elements that represent effects of non-neighboring edge segments are assumed to be zero.