General purpose analog computer

The General Purpose Analog Computer (GPAC)

The General Purpose Analog Computer (GPAC) is a mathematical model of analog computers first introduced in 1941 by Claude Shannon. This model consists of circuits where several basic units are interconnected in order to compute some function. The GPAC can be implemented in practice through the use of mechanical devices or analog electronics. Although analog computers have fallen almost into oblivition due to emergence of the digital computer, it has recently been studied as a way to provide evidence for the Physical Church–Turing thesis. This is because the GPAC is known to also model a large class of dynamical systems defined with ordinary differential equations which appear frequently in the context of Physics. In particular

It is also known to correspond to a large class

These units perform the following basic operations: addition, product, and integration. Moreover there are also units which have as output some predetermined constant. Other operations like difference, quotient, composition, and differentiation can be implemented using only the previous