MOD 4.1

• System Dynamics is a computer-aided approach for strategy and policy design that helps people make better decisions when confronted with complex, dynamic systems.
• The tools used in System Dynamics are models that represent symbolically the reality of the system.
• System dynamics is a simulation modeling language for understanding the behavior of complex dynamic systems.
• System dynamics was created during the mid-1950s by Professor Jay W Forrester of the Massachusetts Institute of Technology.
• A system in System Dynamics is a grouping of interconnected parts to perform a purpose.
• An open system in System Dynamics is characterized by outputs that respond to inputs, but where outputs are isolated from and have no influence over the inputs.
• Feedback systems in System Dynamics have a closed-loop structure that brings results from past action of the system back to control future action, making feedback systems influenced by their own past behavior.
• System dynamics is a method devoted to the study of systems and is thus a tool within the Systems Thinking tool kit.
• System dynamics uses simple graphical notations to model systems: Causal Loop Diagrams and Stock And Flow Diagrams.
• A feedback loop in System Dynamics is the part of a system in which some portion (or all) of the system's output is used as input for future operations.
• Causal loops diagrams (also known as influence diagrams) are used in System Dynamics to display the behavior of cause and effect from a system’s standpoint.
• A causal loop diagram (CLD) in System Dynamics is an illustration that visualizes how variables in a system are causally interrelated.
• Reinforcing loops in System Dynamics are where a change in one direction is compounded by more change.
• Balancing loops in System Dynamics are where a change in one direction is countered by a change in the opposite direction.
• It is a situation to take time before the effect occurs
• A reinforcing or amplifying loop is a loop that leads to growth at an ever-increasing rate.
• In a reinforcing feedback process, a variable continually feeds back upon itself to reinforce its own growth or collapse.
• A balancing or goal-seeking loop is a loop that looks for a goal.
• If the actual state of the variable doesn’t reach the goal, the loop structure pushes its value up.
• If the variable is above goal, the loop pushes it down.
• Balancing loops tend to counteract changes to systems.
• Balancing loops seek goals, provide stability and push towards equilibrium.
• CLD consists of nodes which represent variables and arrows which represent relationships between variables.
• There are several causal loop concepts.
• The arrow is used to show causation.
• This loop is called a positive feedback loop.
• The + sign near the arrowhead signifies that an increase (or decrease) in the first variable leads to an increase (decrease) in the following variable.
• Two hash marks on the causal loop represent a delay.
• It means that the system moves toward equilibrium.
• The symbol R, which is in the middle of a loop, signifies changing direction of the loop.
• The item at the tail of the arrow influences the item at the head of the arrow.
• This loop continues going in the same direction.
• The – sign near the arrowhead signifies that an increase (decreases) in the first variable leads to an decrease(increase) in the following variable.
• This loop is called a negative feedback loop.
• The symbol B, which is in the middle of a loop, signifies that the loop moves away from equilibrium point.