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   John Carlos Baez (johncarlosbaez@mathstodon.xyz)'s status on Thursday, 07-May-2026 03:09:59 JST John Carlos Baez

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   There is by now a useful quantitative theory of items 7-9 on Meadows’ list: that is, the effects of parameters and feedback loops. There are methods to find feedback loops and predict the response of a system to changes in the strength of its feedback loops [G,Ka], determine which nodes in a network have most control over its overall behavior [LSB], and infer parameters from observed data [ROO].

   Less is known about the more impactful items 5 and 6: that is, the response of a system to changes in its structure, such as adding or removing a feedback loop. Important work has been done, from Mason’s gain formula [Mas], to results putting fundamental limits on what additional feedback loops can achieve [SBG], to work on “food web rewiring” of ecosystems in a changing world [Bar,Ma].

   (5/n)

   [G] Goncalves, P. (2006). Eigenvalue and eigenvector analysis of dynamic systems. Proceedings of the 2006 International System Dynamics Conference. Albany, NY: System Dynamics Society. https://proceedings.systemdynamics.org/2006/proceed/papers/GONCA394.pdf

   [Ka] Kampmann, C.E. (2012). Feedback loop gains and system behavior. System Dynamics Review 28(4), 370–95. https://doi.org/10.1002/sdr.1483

   [Mas] Mason, S.J. (1953). Feedback theory: some properties of signal flow graphs. Proceedings of the IRE 41(9), 1144–56.

   [Bar] Bartley, T.J., et al. (2019). Food web rewiring in a changing world. Nature Ecology & Evolution 3(3), 345-354. https://doi.org/10.1038/s41559-018-0772-3

   [Ma] Ma, A., et al. (2025). Network rewiring conserves the topology of drought-impaired food webs. Communications Biology 8(1), 1641. https://doi.org/10.1038/s42003-025-09035-2