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Subsection 3.10.3: Rigid Nodes Up Section 3.10: Boundary Section Section 3.11: Rigid Section

### 3.10.4 Linear Constraints

A linear constraint can be used to couple nodal degrees of freedom. The linear constraint has one dependent degree of freedom , and several independent degrees of freedom . The linear constraint is defined as follows:
Here, the are user-specified scale factors and can be used to specified an offset.
The dependent degree of freedom will be removed from the linear system of equations. Consequently, this nodal degree of freedom should not be used in any other boundary condition.
To define a linear constraint, set the type attribute to linear constraint. The dependent degree of freedom, i.e. the dof that will be removed, is specified via a node number and a dof identifier. Each child dof is defined via the child_dof tag and similarly requires the corresponding node and dof identifier, as well as the value parameter.
<bc type="linear constraint">
<node>5</node>
<dof>x</dof>
<child_dof>
<node>8</node>
<dof>x</dof>
<value>1.0</value>
</child_dof>
<child_dof>
<node>9</node>
<dof>x</dof>
<value>-1.0</value>
</child_dof>
</bc>


Subsection 3.10.3: Rigid Nodes Up Section 3.10: Boundary Section Section 3.11: Rigid Section