GFem language documentation -- 3.7.2 Pde()

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### 3.7.2 Pde()

The syntax for pde is

    pde(u) [+-] op1(u)[*/]exp1 [+-] op2(u)[*/]exp2...=exp3

It defines a partial differential equation with non constant coefficients where `op` is one of the operator:

- `id()`
- `dx()`
- `dy()`
- `laplace()`
- `dxx()`
- `dxy()`
- `dyx()`
- `dyy()`

and where `[*/]` means either a `*` or a `/` and similarly for ±. Note that the expressions are necessarily AFTER the operator while in practice they are between the 2 differentiations for `laplace...dyy` . Thus `laplace(u)*(x+y)` means

.Similarly `dxy(u)*f` means