Two (very simple) bricks allow to add some explicit terms to the tangent system.

The function:

```
indbrick = getfem::add_explicit_matrix(md, varname1, varname2, B
issymmetric = false,
iscoercive = false);
```

adds a brick which just adds the matrix `B` to the tangent system relatively to
the variables `varname1` and `varname2`. The given matrix should have as many
rows as the dimension of `varname1` and as many columns as the dimension of
`varname2`. If the two variables are different and if `issymmetric` is set to
true then the transpose of the matrix is also added to the tangent system (default
is false). Set `iscoercive` to true if the term does not affect the coercivity
of the tangent system (default is false). The matrix can be changed by the
command:

```
getfem::set_private_data_matrix(md, indbrick, B);
```

The function:

```
getfem::add_explicit_rhs(md, varname, L);
```

adds a brick which just add the vector `L` to the right hand side of the tangent
system relatively to the variable `varname`. The given vector should have the
same size as the variable `varname`. The value of the vector can by changed by
the command:

```
getfem::set_private_data_rhs(md, indbrick, L);
```