SYMPHONY's functions are grouped into five independent computational modules. This modular implementation not only facilitates code maintenance, but also allows easy and highly configurable parallelization. Depending on the computational setting, the modules can be compiled as either (1) a single sequential code, (2) a multi-threaded shared-memory parallel code, or (3) separate processes running in distributed fashion over a network. The modules pass data to each other either through shared memory (in the case of sequential computation or shared-memory parallelism) or through a message-passing protocol defined in a separate communications API (in the case of distributed execution). an schematic overview of the modules is presented in Figure 4.4. In the remainder of the section, we describe the modularization scheme and the implementation of each module in a sequential environment.