GFem language documentation -- 3.7.1 Onbdy()

Up: 3.7 Solving an equation
Next: 3.7.2 Pde()

### 3.7.1 Onbdy()

Its purpose is to define a boundary condition for a Partial Differential Equation (PDE).

The general syntax is

    onbdy(ib1, ib2,...) id(u)+<expression>*dnu(u) = g
    onbdy(ib1, ib2,...) u = g

where `ib`'s are boundary identification numbers, `<expression>` is a generic expression and `g` a generic function.

The term `id(u)` may be absent as in `-dnu(u)=g` . `dnu(u)` represents the conormal of the PDE, i.e.

when the PDE operator is