### 5.8.2. RULES File

The `RULES` file contains information about which models and parameters are valid options. This includes `SINGLETON`, `OBJECT` and `PARAMETER` items.

#### 5.8.2.1. RULES

The first items in the `RULES` file list the top level `SINGLETON` objects. All other items are children of these optional top level objects.

- `RULES`: This could be used to modify the list of allowed options. This should always be done locally.

- `LIBRARY`: Includes libraries for materials, reactions, CEL and user routines. Add new materials and reactions using a local library.

- `FLOW`: Contains the current problem definition.

- `USER`: Where user parameters may be stored for later retrieval through User Fortran.

- `COMMAND FILE`: Contains the command file version number.

- `EXECUTION CONTROL`: Contains information about the parallel setup and other settings controlled in the CFX-Solver Manager.

Details about models that are not available can also be found through the user interface. For example, the `SINGLETON: ADVECTION SCHEME` item includes the `QUICK` scheme.

#### 5.8.2.2. SINGLETON

A `SINGLETON` object is permitted to appear once as the child of a parent object. For this reason `SINGLETON` objects do not have names associated with them, for example:

    LIBRARY :
       CEL :
          EXPRESSIONS :

Each of these three items is a `SINGLETON` object. The `LIBRARY SINGLETON` may only have one `CEL SINGLETON`, and the `CEL SINGLETON` may only have one `EXPRESSIONS SINGLETON`. Parameters and child definitions do not need to be grouped for a `SINGLETON` into a single location; this is done automatically by the CFX-Solver. For example, the following is valid:

    LIBRARY :
       CEL :
          EXPRESSIONS :
             myexp1 = 1 [ m ]
          END
       END
    END
    ...
    LIBRARY :
       CEL :
          EXPRESSIONS :
             myexp2 = 2 [ m ]
          END
       END
    END

#### 5.8.2.3. OBJECT

An `OBJECT` is similar to a `SINGLETON` except that more than one can appear as the child of a parent object. For this reason each `OBJECT` must have a name, for example:

    FLOW :
       DOMAIN : domain1
          ...
       END
       DOMAIN : domain2
          ...
       END
    END

Two `OBJECT` items of type `DOMAIN` have been defined with names `domain1` and `domain2`. These are children of the `FLOW SINGLETON`.

#### 5.8.2.4. PARAMETER

A `PARAMETER` consists of a name, followed by the “=” character, followed by a value. Many parameters in the `RULES` file cannot be set in a CCL file and therefore cannot be altered.

- The `Parameter Type` tells you the type of values the parameter is allowed to take. It could be `Real`, `Real List`, `Integer`, `Integer List`, `String` or `String List`. When a list is valid, items should be comma separated.

- Some parameters contain an `Allowed String List`. This contains valid strings that can be used for that parameter.

- Each `PARAMETER` that you can set has a `Dependency List` that lists the variables the `PARAMETER` can depend upon. `XYZ` refers to the x, y and z coordinates. `XYZT` refers to the x, y and z coordinates and time. The CCL file can be edited based on the dependencies listed here.

- If a `PARAMETER` contains the item `Dynamic Reread Item = Yes`, then it can generally be modified while a run is in progress. Some `SINGLETON` objects also contain this item. For details, see Edit Run In Progress Command. Note that you must not change any references to regions while the CFX-Solver is running with topology simplification active; doing so would cause the solver to stop. For details on topology simplification, see the description for expert parameter `topology simplification` in Physical Models Parameters in the CFX-Solver Modeling Guide.

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