ADDITIONAL EXPLANATION: FEEDBACK LOOPS

The web lectures will discuss – among other things- ‘ feedback loops’.  Here is some explanation  in advance.

A feedback loop consists of two or more causal influences between elements that are connected in such a way that if one follows the causality starting at any element in the loop, one eventually returns to the first element. Or in other words, if a change in variable A directly causes a change.

Positive feedback loop

A feedback loop is called positive or reinforcing in an initial increase in our variable A leads after some time to an additional increase in A and so on, and that an initial decrease in A leads to an additional decrease in A and so on and so on. In isolation, such feedback loops generate exponentially escalating behavior which could be (extremely) beneficial or (extremely) detrimental. The term ‘positive’ should therefore not be confused with its everyday connotation. Undesirable positive feedback loops are also known as vicious circles.

Negative feedback loop

A feedback loop is called negative or balancing if an initial increase in variable A leads after some time to a decrease in A, and that an initial decrease in A leads to an increase in A. In isolation, such feedback loops generate damping or goal-oriented behaviour to goal levels. They could be used for automatic control/balancing of systems of processes. The presence of a negative feedback loop does not imply that the objective is automatically achieved or that the process is under control. In some feedback loop systems, a negative feedback may actually lead to undesirable behavior, for example to undesirable damping or oscillatory behavior. 

Recource: Continuous Systems models II: System Dynamics Lecture Notes, Pruyt  et al. , 2009, Delft University of Technology. 

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