Conceptual Questions

	What is Feedback?
	What is the difference between discrete and continuous simulation?
	What is Systems Thinking?
	What is a Causal Loop Diagram?
	What is an Archetype?
	What is a Simulation?
	What is System Dynamics?
	What are Management Flight Simulators, or Learning Environments?

If you have further questions, please email us at faq@vensim.com

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What is Feedback?

Feedback is a process in which a decision or action causes changes to occur which, after a time, cause a revision of the decision or action. For example, if you are trying to catch a person running in front of you it is necessary to run faster till you get beside them and then slow down to match their pace. Though feedback is a very simple concept, its implications can be quite surprising. Feedback loops typically involve more than one person or organization, each responding to the actions of another in such a way as to, eventually, change the behavior of others. Arms races, stock market bubbles, inner city degradation, and instability in manufacturing volume requirements are all examples of behaviors that result from feedback. Diagram of a feedback loop Back to top

What is the difference between discrete and continuous?

Technically, Vensim and other system dynamics packages are capable of solving systems of lumped ordinary difference or differential equations. We often refer to Vensim as supporting continuous simulation. What this means is that it is best suited to situations where most of the variables change continuously, and not in increments. This is to be contrasted with discrete event simulation in which individual entities are tracked and the results added up to report behavior. While it is possible to make discrete variables in Vensim, this is usually only sensible if there are a small number of such variables relative to everything else in the model.
A discrete event simulation moves forward by allowing each entity to choose the next time it needs to do something (be fully assembled, change to a different workstation, and so on). For this type of modeling it is desirable to have a clock that jumps from time to time and only does the things that need doing at that time. It is possible to make Time jump from place to place in Vensim. However at each time everything gets done. This is very inefficient for discrete even style simulation where only one out of say 100,000 things might need to be computed. Back to top

What is Systems Thinking?

Systems thinking is a general term for looking at things systemically and thinking in terms of feedback. One of the major tools of systems thinking is the causal loop diagram, and another is the system archetype. The term systems thinking was made popular by the publication of the book The Fifth Discipline by Peter Senge. Some people consider systems thinking to be broader than this, including such concepts as double loop learning as developed by Argyris. Back to top

What is a Causal Loop Diagram?

A causal loop diagram is a picture containing words and directed arrows connecting those words, usually with at least one closed loop representing feedback. Causal loop diagrams can easily be created using a pencil and paper. Vensim supports the creation and analysis of causal loop diagrams. Causal Loop diagram Back to top

What is an Archetype?

An archetype is an abstraction of a feedback structure that is known to generate a particular type of behavior. For example, escalation is an archetype in which two organizations try to exceed a capability of the other and end up simultaneously growing that capability. An arms race is an example of the escalation archetype. Archetypes were made popular in The Fifth Discipline. Back to top

What is a Simulation?

A simulation is a calculation of the implications of all the relationships that have been specified for the variables in a model. Simulations in Vensim result in the behavior (over time) of all the variables in the model. These results are normally reviewed as time graphs or tables. Back to top

What is System Dynamics?

System Dynamics is the study and analysis of dynamic feedback systems using computer simulation. The field of system dynamics has been developed from the work of Jay Forrester to integrate engineering techniques for understanding feedback control systems into the study of social and business policy. For more information, see the Resources page or the web site for The System Dynamics Society. Back to top

What are Management Flight Simulators, or Learning Environments?

These go by various names, including learning environments, management simulators, custom applications, Vensim applications (Venapps) and more. They are a simplified interface which allows an inexperienced user limited access to a simulation model. Learning environments allow the user a few choices to set up or run a model, and present output information in a custom interface, without the need to learn specialized modeling software. Environments can be designed to run a model through a full simulation time period, or they can be designed to allow the user to step through a simulation at certain time intervals. In this fashion, a user can change constant values during the simulation to try and "control" a system. In Vensim, this is called playing a "Game" and Vensim is run in gaming mode. Read more about Vensim applications