[1] This model consists of circuits where several basic units are interconnected in order to compute some function.
[2] This is because the GPAC is also known to model a large class of dynamical systems defined with ordinary differential equations, which appear frequently in the context of physics.
[5] The General Purpose Analog Computer was originally introduced by Claude Shannon.
[1] This model came as a result of his work on Vannevar Bush's differential analyzer, an early analog computer.
More recently, and for simplicity, the GPAC has instead been defined using the equivalent four types of units: adders, multipliers, integrators and real constant units (which always output the value k, for some fixed real number k).