Pair Feature

) is a special feature that defines conditions on pairs. A pair has a source and a destination side, and a pair condition typically connects the dependent variables between them using pointwise constraints.

	The most common pair condition is the continuity pair condition, which simply makes the dependent variables equal on both sides. All physics interfaces gets this pair condition by default, so you do not have to add it.

This feature is useful to define other types of pair conditions. The major difference between a pair feature and an ordinary feature lies in subnodes that define selections.

For pair features, there are two extra options in the list of the section; and . With these options you can specify to use the source or destination boundaries in the condition of a pair feature; see Specifying Selections for more information.

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To add a under the branch, node: On the toolbar, select it from the menu, or right-click and add it from the context menu.

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To add a under the or , Right-click the or nodes to add this from the submenu.

Except for a few excluded sections, the window is similar to the Generic Feature node.

See Selection Settings for . For a pair feature, you do not have to specify the geometric entity level, because it is always boundary level. The same is true for the domain type setting, because all pairs belong to a special domain type, called . Ordinary features that support this domain type also appear in a pair version among the physics interface’s pair conditions.

All pair features also have a special rule for overriding selections. They are always exclusive to all nonpair features preceding the pair in the list. For all features, pairs and nonpairs that lie below the pair in the list, contribute with the pair condition. As a result, you cannot set the override type for pair features.

Select the check box to turn off the automatic looping over pairs, so no individual pair access is supported for the nodes under the pair feature and for links to normal components. Any pair looping then have to use an explicit pair looping with a component (see the list in Component).

Select the check box if the physics interface only allows a single instance of the feature.

For features under a physics interface there is an check box. Select this check box if you want the feature to be a default feature. When you specify default features, specify the geometric entity level in the list. Newly created interfaces then add the feature on this level. The specifies the entity types the default feature is added on.

In the table, you can specify special options for the default feature. By default, default features have a selection over all domains (it cannot be changed), and you can neither remove or disable the feature. Select the check box columns — , , , and — to alter this default behavior. The last column, , is a preference to control the order of the default features. The standard order is domain features first, then boundary features, and so on until the point features followed by the global features. The automatically added initial value features always show up last in the list. The program uses a integer when sorting the default features. The integer depends on the geometric entity dimension and the list order weight using the following formula: