Constraint

The Constraint boundary condition specifies an expression R which is constrained to be equal to zero on the selection, R = 0. By default, this is a bidirectional constraint, meaning that all variables in R are affected by reaction terms.

Constraint

Enter a value or expression for the value of R in the constraint R = 0. For example, to constrain u to 2, enter 2-u in the field for R.

The sign in front of u in the constraint controls the sign of the implicit Lagrange multiplier μ, as well as the sign of reaction forces computed using the reacf() operator. For consistency with the way predefined physics interfaces implement constraints, write 2-u rather than u-2 in R.

Constraint Settings

To display this section, click the Show button () and select Advanced Physics Options. Normally these settings do not need to be changed. This section contains settings for specifying the type of constraint and whether to use a pointwise or weak constraint. See Constraint Settings for more information.

You can add subnodes to exclude the constraint from any surrounding boundary, edge, or point. See Excluded Points, Excluded Edges, Excluded Surfaces.

See Coefficient Form PDE for all the settings and Compact and Standard Notations for Classical PDEs for the equations that the Classical PDE interface solve.