10 DOLFIN : a C + + / Python finite element library

A large part of the functionality of FEniCS is implemented as part of DOLFIN. It provides a problem solving environment for models based on partial differential equations and implements core parts of the functionality of FEniCS, including data structures and algorithms for computational meshes and finite element assembly. To provide a simple and consistent user interface, DOLFIN wraps the functionality of other FEniCS components and external software, and handles the communication between these components. Figure 10.1 presents an overview of the relationships between the components of FEniCS and external software. The software map presented in the figure shows a user application implemented on top of the DOLFIN user interface, either in C++ or in Python. User applications may also be developed using FEniCS Apps, a collection of solvers implemented on top of FEniCS/DOLFIN. DOLFIN itself functions as both a user interface and a core component of FEniCS. All communication between a user program, other core components of FEniCS and external software is routed through wrapper layers that are implemented as part of the DOLFIN user interface. In particular, variational forms expressed in the UFL form language (Chapter 17) are passed to the form compiler FFC (Chapter 11) or SFC (Chapter 15) to generate UFC code (Chapter 16), which can then be used by DOLFIN to assemble linear systems. In the case of FFC, this code generation depends on the finite element backend FIAT (Chapter 13), the just-in-time compilation utility Instant (Chapter 14) and the optional optimizing backend FErari (Chapter 12). Finally, the plotting capabilities provided by DOLFIN are implemented by Viper. Some of this communication is exposed to users of the DOLFIN C++ interface, which requires a user to explicitly generate UFC code from a UFL form file by calling a form compiler on the command-line. DOLFIN also relies on external software for important functionality such as the linear algebra libraries PETSc, Trilinos, uBLAS and MTL4, and the mesh partitioning libraries ParMETIS and SCOTCH (Pellegrini).