Fig.2summarizes this layout for the general case, after the initial steps. While in Fig.1, there is a separate drawing for each time step, all these drawings appear overlaid in Fig.2. More precisely, each column in Fig.2corresponds to one of the chunks (indexed here j −4to j +1), and the time steps are characterized by the shading, thatis, rectangles with identical fill patterns represent sets of processors working simultaneously. The solid black rectangles represent the set of processors working in parallel at time j +logn: half of them on chunkj, aquarter on chunkj −1, etc. The solid grey rectangles are the working processors in the following step, attime j +logn +1.