# Loop

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A **loop** is a closed path that returns to its starting node without passing through any node more than once. Common examples are feedback systems.

Loops are defined as *positive*, if the number of negative relationships is even. They are called negative if the structure contains an odd number of negative correlators.^{[1]}

Negative loops are stable systems, positive loops are unstable.

The structure shown in the right contains three loops (ABCDA, BCDB and ABCEA). In this example on the left the loops ABCDA and ABCEA are positive; The loop BCDB is negative.

## References Edit

- ↑ 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

## Additional information Edit

- Franklin GF, Powell JD, Emami-Naeini A. Feedback Control of Dynamic Systems. Delhi: Pearson Education, 2002. ISBN 8178086751