**CERIG**, * MASTE*,

`SLAVE`

`Ldof`

`Ldof2`

`Ldof3`

`Ldof4`

`Ldof5`

Compatible Products: – | Pro | Premium | Enterprise | Ent PP | Ent Solver | DYNA

`MASTE`

Retained (or master) node for this rigid region. If

= P, then graphical picking of the master and slave nodes is enabled (first node picked will be the master node, and subsequent nodes picked will be slave nodes), and subsequent fields are ignored (valid only in GUI).`MASTE`

`SLAVE`

Removed (or slave) node for this rigid region. If ALL, slave nodes are all selected nodes.

`Ldof`

Degrees of freedom associated with equations:

**ALL**—

All applicable degrees of freedom (default). If 3-D, generate 6 equations based on UX, UY, UZ, ROTX, ROTY, ROTZ; if 2-D, generate 3 equations based on UX, UY, ROTZ.

**UXYZ**—

Translational degrees of freedom. If 3-D, generate 3 equations based on the slave nodes' UX, UY, and UZ DOFs and the master node's UX, UY, UZ, ROTX, ROTY, and ROTZ DOFs; if 2-D, generate 2 equations based on the slave nodes UX and UY DOFs and the master nodes UX, UY, and ROTZ DOFs. No equations are generated for the rotational coupling.

**RXYZ**—

Rotational degrees of freedom. If 3-D, generate 3 equations based on ROTX, ROTY, ROTZ; if 2-D, generate 1 equation based on ROTZ. No equations are generated for the translational coupling.

**UX**—

Slave translational UX degree of freedom only.

**UY**—

Slave translational UY degree of freedom only.

**UZ**—

Slave translational UZ degree of freedom only.

**ROTX**—

Slave rotational ROTX degree of freedom only.

**ROTY**—

Slave rotational ROTY degree of freedom only.

**ROTZ**—

Slave rotational ROTZ degree of freedom only.

,`Ldof2`

,`Ldof3`

,`Ldof4`

`Ldof5`

Additional degrees of freedom. Used only if more than one degree of freedom required and

is not ALL, UXYZ, or RXYZ.`Ldof`

Defines a rigid region (link, area or volume) by automatically
generating constraint equations to relate nodes in the region. Nodes
in the rigid region must be assigned a geometric location before this
command is used. Also, nodes must be connected to elements having
the required degree of freedom set (see * Ldof* above). Generated constraint equations are based on small deflection
theory. Generated constraint equations are numbered beginning from
the highest previously defined equation number (

`NEQN`

This command will generate the constraint equations needed for
defining rigid lines in 2-D or 3-D space. Multiple rigid lines relative
to a common point are used to define a rigid area or a rigid volume.
In 2-D space, with * Ldof = *ALL, three equations
are generated for each pair of constrained nodes. These equations
define the three rigid body motions in global Cartesian space, i.e.,
two in-plane translations and one in-plane rotation. These equations
assume the X-Y plane to be the active plane with UX, UY, and ROTZ
degrees of freedom available at each node. Other types of equations
can be generated with the appropriate

`Ldof`

Six equations are generated for each pair of constrained nodes
in 3-D space (with * Ldof = *ALL). These
equations define the six rigid body motions in global Cartesian space.
These equations assume that UX, UY, UZ, ROTX, ROTY, and ROTZ degrees
of freedom are available at each node.

The UXYZ label allows generating a partial set of rigid region equations. This option is useful for transmitting the bending moment between elements having different degrees of freedom at a node. With this option only two of the three equations are generated for each pair of constrained nodes in 2-D space. In 3-D space, only three of the six equations are generated. In each case the rotational coupling equations are not generated. Similarly, the RXYZ label allows generating a partial set of equations with the translational coupling equations omitted.

Applying this command to a large number of slave nodes may result in constraint equations with a large number of coefficients. This may significantly increase the peak memory required during the process of element assembly. If real memory or virtual memory is not available, consider reducing the number of slave nodes.

Note that under certain circumstances the
constraint equations generated by **CERIG** may be
modified during the solution. See Program Modification of Constraint Equations for more information.

As an alternative to the **CERIG** command, you
can define a similar type of rigid region using contact elements and
the internal multipoint constraint (MPC) algorithm. See Surface-Based Constraints for more information.

**CERIG** cannot be deleted using **CEDELE**,ALL and then regenerated in the second or higher load steps if the **LSWRITE** and **LSSOLVE** procedure is used. **CERIG** writes constraint equations directly into load step
files. Deleting constraint equations (**CEDELE**,ALL)
cannot always maintain the consistency among load steps.