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Lattice gas automata or lattice gas cellular automata are a type of cellular automaton used to simulate fluid flows. They were the precursor to the lattice Boltzmann methods. From lattice gas automata, it is possible to derive the macroscopic Navier-Stokes equations.〔Succi, section 2.3 describes the process〕 Interest in lattice gas automaton methods levelled off in the early 1990s, as the interest in the lattice Boltzmann started to rise.〔Succi, section 2.6〕 ==Basic principles== As a cellular automaton, these models comprise a lattice, where the sites on the lattice can take a certain number of different states. In lattice gas, the various states are particles with certain velocities. Evolution of the simulation is done in discrete time steps. After each time step, the state at a given site can be determined by the state of the site itself and neighboring sites, ''before'' the time step. The state at each site is purely boolean. At a given site, there either ''is'' or ''is not'' a particle moving in each direction. At each time step, two processes are carried out, propagation and collision.〔Buick, section 3.4〕 In the propagation step, each particle will move to a neighboring site determined by the velocity that particle had. Barring any collisions, a particle with an upwards velocity will after the time step maintain that velocity, but be moved to the neighboring site above the original site. The so-called exclusion principle prevents two or more particles from travelling on the same link in the same direction. In the collision step, collision rules are used to determine what happens if multiple particles reach the same site. These collision rules are required to maintain mass conservation, and conserve the total momentum; the block cellular automaton model can be used to achieve these conservation laws.〔.〕 Note that the exclusion principle does not prevent two particles from travelling on the same link in ''opposite'' directions, when this happens, the two particles pass each other without colliding. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「lattice gas automaton」の詳細全文を読む スポンサード リンク
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