Model behaviour and the concept of loop impact: A practical method

Abstract

Quantifying the strengths of feedback loops can bring insight into the way the structure of a system dynamics model helps determine behaviour. This paper proposes the concept of loop impact, using the functional relationship between the second and first derivative from the Pathway Participation Metric method, and describes a numerical method to derive the impacts of feedback loops within a system dynamics model. An algorithm is presented that will identify which loop, or loop combination, explains stock behaviour. The method is applied to the yeast, epidemic and market growth models and compared with previous work. It is shown that the method can deal with loops that change polarity, hidden loops and those that self cancel. A procedure is set out to calculate impacts when loops have junctions and graphical converters. It is anticipated that the method will be adopted by system dynamicists and applied to a broader range of models. Copyright © 2014 System Dynamics Society

Identification of Sustainability Key Factors Based on Capturing Dominant Feedbacks of Behavioural Stereotypes in Socio-Economic Systems

“…Only then, an estimation of dominant feedbacks can be performed. This is not a simple task and still represents an actual topic in the system dynamics research [51]. The problem is that this type of dynamic is not connected with the usage of exact values of constants or variables.…”

A robust data-driven macro-socioeconomic-energy model

“…In addition, we have flows not from (or to) stocks that we distinguish by referring to as auxiliaries. We use iterative time-stepped simulation to evolve the model of the system forward in time with equations representing influences -in representing any complex system some of these influences will form feedback loops (Hayward and Boswell, 2014;Mollerup et al, 2015). Thus we are dealing with a dynamical system model in which the interplay of positive and negative feedback mechanisms will drive system behaviour (Kelly et al, 2013).…”

Using R libraries to facilitate sensitivity analysis and to calibrate system dynamics models

“…The model is based on the one‐stock limits‐to‐growth model for business structures (Mojtahedzadeh et al ., ), which has also been used as an exemplar for illustrating the loop impact method (Hayward and Boswell, ). The stock‐and‐flow structure, with feedbacks, is shown in Figure .…”