Implicit equations are those where the dependent variables rely on the values of one another from the *current* time. In other words, all dependent variables must be solved *simultaneously*, which is only possible using an *iterative method*.

OpenFOAM's fvm namespace defines implicit operations.

Implicit methods have a less stringent timestep size restriction than explicit methods. Therefore they are preferable for steady-state problems, since a steady state problem can be viewed as a transient problem with an infinite timestep.

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