系统动力学(名词解释)

名词解释：
System Dynamics：A powerful methodology for framing, understanding, and discussing complex policy issues and problems,is a methodology for studying and managing complex feedback systems, such as one finds in business and other social systems.
Mental models:are the images (attitudes and assumptions) we carry in our minds about ourselves, other people, institutions, and every aspect of the world which guide our interpretations and behavior.
System:The behavior of a system depends not only on the behavior of the components of a system but also on how these components interact.
System dynamics:is the application of systems theory to the behavior of complex systems. complex systems:are systems in which there are multiple interactions between many different components (or agents).
dynamic hypothesis:Once the problem has been identified and characterized over an appropriate time, modeler must develop a theory called “dynamic hypothesis”that accounts for the problematic behavior.
Chaos:When the present determines the future, but the approximate present does not approximately determine the future
limit cycles:If an oscillatory system with a locally unstable equilibrium is given a slight nudge off its equilibrium point, its swings grow larger and larger until they are constrained by various nonlinearities. Such oscillations are known as limit cycles.
dynamic complexity:The complexity generated by the interactive-feedback causality
directed graph:It is a graph, or set of nodes connected by edges, where the edges have a direction associated with them.
Cause and effect :is a simple idea in which actions and decisions have consequences, Feedback: is the process in which an action taken by a person or thing will eventually affect that person or thing.
Feedback loop: is a closed sequence of causes and effects
简答：
1.The problem of system dynamics has the following four characteristics:
Complexity: On one hand many factors are included in the system; on the other hand these factors in the given system are connected with each other.
Dynamics: Dynamic characteristics reflect the developing and changing laws of nature.
Nonlinearity. Nonlinear characteristics are important relationships among many factors in system dynamics.
Time lag: It describes a situation where the system or a certain part of the system only change after a period of time under the input.
2.Steps of the modeling process
Step 1 Problem Articulation (Boundary Selection):Theme selection, Key variables, Time horizon, Dynamic problem definition (reference modes).
Step 2 Formulation of Dynamic Hypothesis:Initial hypothesis generation, Endogenous focus,
Mapping.
Step 3 Formulation of a Simulation Model:Specification, Estimation, Tests.
Step 4 Testing:Comparison to reference modes, Robustness under extreme conditions, Sensitivity. Step 5 Policy Design and Evaluation:Scenario specification, Policy design, “What if. . .”analysis, Sensitivity analysis, Interactions of policies.
3.Characteristics of Complex Systems
Tightly Coupled (“Everything influences everything else”,“You can’t just do one thing”) Dynamic (Change occurs at many time scales)
Policy Resistant (Many obvious solutions to problems fail or actually worsen the situation.) Counterintuitive (Cause and effect are distant in time and space)
Exhibit Tradeoffs (Long term behavior is often different from short term behavior)
4.Why are models useful?
1)Creating a model forces one to better understand the real system. Models can help explain observations and help guide the development of future experiments.
2)Models can be extremely useful in explaining how a system works to yourself and to others.
3)Experiments can be performed to help understand the response of a system to changes without harming the real system.
4)A model is the only method that one can use to estimate the future behavior of a system to past, present, and future processes that may influence a system.
5)Models can be extremely helpful in policy development.
5.4 types of cause contribute explain a phenomenon
1) Material cause: the substance that made it so
2)Efficient cause: the direct efforts that made it so
3)Formal cause: the plan or agent that made it so
4)Final cause: the ultimate purpose for being so。