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User-written Functions

The majority of the user functions are called from either the master process or the LP process. For these two modules, user functions are invoked from so-called wrapper functions that provide the interface. Each wrapper function is named *_u() , where * is the name of the corresponding user function, and is defined in a file called *_wrapper.c. The wrapper function first collects the necessary data and hands it to the user by calling the user function. Based on the return value from the user, the wrapper then performs any necessary post-processing. Most user functions are designed so that the user can do as little or as much as she likes. Where it is feasible, there are default options that allow the user to do nothing if the default behavior is acceptable. This is not possible in all cases and the user must provide certain functions, such as separation.

In the next section, the user functions will be described in detail. The name of every user written function starts with user_. There are three kinds of arguments:

IN:

An argument containing information that the user might need to perform the function.

OUT:

A pointer to an argument in which the user should return a result (requested data, decision, etc.) of the function.

INOUT:

An argument which contains information the user might need, but also for which the user can change the value.

The return values from each function are as follows:

Return values:

Notes:

• Sometimes an output is optional. This will always be noted in the function descriptions.
• If an array has to be returned (i.e., the argument is type **array) then (unless otherwise noted) the user has to allocate space for the array itself and set *array to be the array allocated. If an output array is optional then the user must not set *array for the array she is not going to fill up because this is how SYMPHONY decides which optional arrays are filled up.
• Some built-in options are implemented so that the user can invoke them directly from the user function. This might be useful if, for example, the user wants to use different built-in options at different stages of the algorithm, or if he wants to do the post-processing himself but does not want to implement the option itself.