**German**: Rückkoppelung

A system whose output acts modulatory back to its input is referred to as **feedback** mechanism, e.g. as degenerative feedback in feedback control systems.

In degenerative feedback loops (also referred to as negative feedback as time differentials of deviations from equilibrium are negative) the output signal is apt to inhibit the system's input, whereas in positive feedback (regenerative feedback processes) the output amplifies the input signal.

Feedback loops are defined as positive (regenerative) if the number of negative correlators is even (including 0). If the number of negative correlators is odd the loop is negative (degenerative).^{[1]} Degenerative systems are stable systems, regenerative systems exhibit unstable behaviour.

Cybernetic systems theory mathematically analyses feedback processes.

## References[]

- ↑ Juan Martín García (2011),
*Theory and Practical Exercises of System Dynamics*, Barcelona, Spain: Juan Martín García, ISBN 8460998045, 8460998045, http://openlibrary.org/books/OL25175096M/Theory_and_Practical_Exercises_of_System_Dynamics