V.S. Kouikoglou, Y.A. Phillis," On the monotonicity of hierarchical sum–product fuzzy systems," Fuzzy sets and syst.,vol.160,no. 24, pp.3530-3538,Dec. 2009.doi:10.1016/j.fss.2009.02.001
https://doi.org/10.1016/j.fss.2009.02.001
Motivated by the authors’ previous work on the control of queueing systems, the assessment of sustainable development, and the measurement of material recyclability, this paper provides sufficient conditions on the parameters of hierarchical fuzzy systems under which the output of the system is monotonic with respect to its inputs. This property could be useful in designing multistage fuzzy inference systems and fuzzy controllers.