Stanford Linear Accelerator Center ]:_92 014837 Stanford University, Stanford, CA From the beginning at Los Alamos, solutions to the transport equation were very important. Ali sorts of approximate solution techniques, including one by Feynman1 were developed to help design nuclear weapons but are now long forgotten. Most of these methods were based on the methods of mathematical physics familiar to the project physicists and predated the use of computers, but continued research coupled with

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... ssing need produced two new and powerful computer-based systems: Monte Carlo and the Sn Method. The healthy and long-term competition between the two Los Alamos groups responsible for these quite different approaches was both stimulating and synergistic. By the mid-1950's, Bengt Carlson had in place ali the elements of his Sn system. While the Sn method is often referred to as a discrete ordinates method, which it is because the angular variable is represented by an ensemble of discrete directions, it is more appropriate to refer to Bengt's creation as a system, that is, as an integrated whole based on a set of consistent themes. Using the multigroup formulation as a starting place, these themes included 1. insistence on particle-conserving difference schemes, 2. finite difference approximations of uniform accuracy but of the utmost simplicity for speed of evaluation, *