Function Builders

The function builders can be found in the function_builders directory alongside a base class and a factory implementation.

Base Class (

The base class defines some shared interfaces for all of the function builders, and should be inheritted from for a new function builder to work.

In general, the only requirement for the sub classes of this are that they override the abstract build method so that it returns a firedrake Function, or a numerical value. In practice, since this is designed to only be accessed by the factory (explained below), there are additional constraints:

  • Function builders should not modify the signature of __init__. E.g. they are initialised with (mesh, V) and any other arguments must be defined using the assign method.
  • The signature of build should not be edited. To access arguments for constructing a function, the object dictionary _props should be used.

Since the build method signature cannot be changed, values must be passed through a different mechanism. This is done using the _props dictionary and assign method.

Assign takes a name and a value as inputs, it then checks this pair is valid for the class by checking that the name is in the properties dictionary and that the type of value matches the entry in properties. If it is valid, _props is updated with the name-value pair.

Factory (

The factory is used to dynamically import and use only the specified function builder at runtime. This means that extending the set of function builders is done by creating a new file. The factory will then be able to find the new builder by name and load the code.

In order for the factory to work, there can only be 1 function builder per file.

Function Builders (<type>

The rest of the files in this directory are function builders and should serve as good examples for adding new ones.

To create a new function builder, you should make sure to define the following on the new subclass:

  • properties dict: This dictionary should have the names of all properties that are required to build a function, alongside the type of each property. Types can be specified as a tuple e.g. if a value can be int or float.
  • build method: This is the main logic in the builder.

It is also important to name the file sensibly as this is how the function builder will be selected. For a file called, the user will be required to set the type in the config file to foo. If this is not appropriate in the future, the factory will have to be changed.