A lattice Boltzmann method (LBM) is any of a class of computational fluid dynamics (CFD) methods that treat the fluid as particles, not simulating every molecule, but simulating the fluid using a smaller number of imaginary particles that interact in a way that produces the fluid's characteristics. (Computing the travel of every molecule would be computationally intractable.) Also, it handles both space and particle velocity in discrete steps. An advantage of the method is that it allows reasonable simulation of changes between a substance's liquid and gaseous states, e.g., a surface between the liquid and an atmosphere. Another is that it works well with parallel computation, meaning that the parallel-processing ability of supercomputers effectively speeds up computation. The general strategy includes alternating between types of steps, one to move the particles, and the next (termed relaxation) to simulate the effect of collisions.