In \Dumux two sorts of models are implemented: Fully-coupled models and decoupled models. In the fully-coupled models a flow system is described by a system of strongly coupled equations, which can be for example mass balance equations for phases, mass balance equations for components or energy balance equations. In contrast, a decoupled model consists of a pressure equation, which is iteratively coupled to a saturation equation, concentration equations, energy balance equations, etc.
Examples for different kinds of both, coupled and decoupled models, are isothermal two-phase models, isothermal two-phase two-component models, non-isothermal two-phase models and non-isothermal two-phase two-component models.
In section \ref{box} a short introduction to the box method is given. The box method is used in the fully-coupled models for the spatial discretization of the system of equations. The decoupled models employ usually a cell-centered finite volume scheme. The following two sections of the tutorial demonstrate how to solve problems using, first, a fully-coupled model (section \ref{tutorial-coupled}) and, second, using a decoupled model (section \ref{tutorial-decoupled}). Being the easiest case, an isothermal two-phase system (two fluid phases, one solid phase) will be considered.
