When using Fasttalk to specify PDE problems, a key attribute is the first letter of the statement. The code e denotes that the statement specifies the equation in the PDE problem. This equation is allowed to have multiple components. The terms in the equation are described in a mathematical language which allows derivative operators, expressions involving parameters and known vectors, and unknowns. In all, 38 distinct derivative expressions are provided in Fastflo; they comprise a thorough list of tensor expressions encountered when solving second-order PDEs by the finite element method. The full list of derivative expressions is given at the end of this chapter.
The code b indicates boundary conditions. Each of these has a tag, linking boundary conditions to tagged sections of the boundary. There are special expressions for the common types of boundary conditions, and also the same expressions as those available for PDEs, thus enabling complicated expressions to be incorporated into boundary conditions.
Other specialised statement codes are
| A | for announcing problems |
| D | for making aliases |
| F | for file inclusions |
| N | for naming vectors |
| P | for defining parameters |