# Constraint brick¶

The constraint brick allows to add an explicit constraint on a variable. Explicit means that no integration is done. if $$U$$ is a variable then a constraint of the type

$BU = L,$

can be added with the two following functions:

indbrick = getfem::add_constraint_with_penalization(md, varname,
penalisation_coeff, B, L);
multname, B, L);


In the second case, a (fixed size) variable which will serve as a multiplier should be first added to the model.

For the penalized version B should not contain a plain row, otherwise the whole tangent matrix will be plain. The penalization parameter can be changed thanks to the function:

change_penalization_coeff(md, ind_brick, penalisation_coeff);


It is possible to change the constraints at any time thanks to the two following functions:

getfem::set_private_data_matrix(md, indbrick, B)
getfem::set_private_data_rhs(md, indbrick, L)


where indbrick is the index of the brick in the model.