Courant Fredericks Levy condition

The Courant-Friedrichs-Levy Condition (CFL condition), says that in any time-marching computer simulation, the time step must be less than the time for some significant action to occur, and preferably considerably less.

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For example, if a wave is crossing a discrete grid, then the timestep must be less than the time for the wave to traval adjacent grid points. As a corollary, when the grid point separation is reduced, the upper limit for the time step also decreases.

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This can be a very limiting constraint and efforts are often made to avoid it by using an implicit solution.

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