**CE**, * NEQN*,

`CONST`

`NODE1`

`Lab1`

`C1`

`NODE2`

`Lab2`

`C2`

`NODE3`

`Lab3`

`C3`

MP ME ST PR PRN <> EM DY PP EME MFS

`NEQN`

Set equation reference number:

**n**— Arbitrary set number.

**HIGH**— The highest defined constraint equation number. This option is especially useful when adding nodes to an existing set.

**NEXT**— The highest defined constraint equation number plus one. This option automatically numbers coupled sets so that existing sets are not modified.

The default value is HIGH.

`CONST`

Constant term of equation.

`NODE1`

Node for first term of equation. If -

, this term is deleted from the equation.`NODE1`

`Lab1`

Degree of freedom label for first term of equation. Structural labels: UX, UY, or UZ (displacements); ROTX, ROTY, or ROTZ (rotations, in radians). Thermal labels: TEMP, TBOT, TE2, TE3, . . ., TTOP (temperature). Electric labels: VOLT (voltage). Magnetic labels: MAG (scalar magnetic potential); AX, AY, or AZ (vector magnetic potentials). Diffusion label: CONC (concentration).

`C1`

Coefficient for first node term of equation. If zero, this term is ignored.

,`NODE2`

,`Lab2`

`C2`

Node, label, and coefficient for second term.

,`NODE3`

,`Lab3`

`C3`

Node, label, and coefficient for third term.

Repeat the **CE** command to add additional terms
to the same equation. To change only the constant term, repeat the
command with no node terms specified. Only the constant term can
be changed during solution, and only with the **CECMOD** command.

Linear constraint equations may be used to relate the degrees
of freedom of selected nodes in a more general manner than described
for nodal coupling [**CP**]. The constraint equation
is of the form:

where U(I) is the degree of freedom (displacement, temperature, etc.) of term (I). The following example is a set of two constraint equations, each containing three terms:

0.0 = 3.0* (1 UX) + 3.0* (4 UX) + (-2.0)* (4 ROTY)

2.0 = 6.0* (2 UX) + 10.0* (4 UY) + 1.0* (3 UZ)

The first unique degree of freedom in the equation is eliminated in terms of all other degrees of freedom in the equation. A unique degree of freedom is one which is not specified in any other constraint equation, coupled node set, specified displacement set, or master degree of freedom set. It is recommended that the first term of the equation be the degree of freedom to be eliminated. The first term of the equation cannot contain a master degree of freedom, and no term can contain coupled degrees of freedom. The same degree of freedom may be specified in more than one equation but care must be taken to avoid over-specification (over-constraint).

The degrees of freedom specified in the equation (i.e., UX,
UY, ROTZ, etc.) must also be included in the model (as determined
from the element types [**ET**]). Also, each node
in the equation must be defined on an element (any element type containing
that degree of freedom will do).

For buckling and modal analyses, the constant term of the equation
will not be taken into account (that is, * CONST* is always zero).

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