CPH:CC - systems thinking

A system response that is greater than is seemingly implied by input causes. Occurs in information-feedback systems when policies adjust levels to values that change w/ varying flow rates. Associated w/ delays, order/inventory processes, forecasting, etc.

Amplification

Goal seeking behavior produced by negative feedback.

Asymptomatic growth/decay

A system that functions w/o any exogenous variables generated outside the model. The system internally generates the values of all the variables through time by their interactions.

Closed system

A set of descriptions that tell the computer how each part of the system acts. Captures the dynamic essence of the system it represents.

Computer model

The building blocks that carry information from one element in a model to another element. "information" may be a constant, an algebraic relationship, graphical relationship, or quantity.

Connector

The fives steps of constructing a causal loop diagram are:

1. choose variables 2. link variables w/ arrows pointing from cause to effect 3. assign a direction of effect (same or opposite) to each link 4. indicate delays 5. assign polarity to overall loop

The collection of some quantity over time.

Accumulation

The incorporation of numerous distinct system components into one variable. Done for simplicity when combination generates the same behavior of interest representing the components separately.

Aggregation

An equation that take the PV of variables to compute the PV of an auxiliary variable. Part of a rate equation connecting a level to a rate. Embody unit consistency and are symbolized by a circle in a flow equation.

Auxiliary equation / variable

A loop that seeks equilibrium - tries to bring stocks to a desired state and keep them there. Limits and constrains, and is also called a negative loop.

Balancing loop

A system dynamics tool that shows how certain variables change over time. Several variables can appear on the same graph for comparison.

Behavior over time diagram

Border enclosing only the parts of the system structure needed to generate the behavior of interest. excludes all components not relevant to the problem behavior of the system.

Boundary / system boundary

Diagram representing a closed loop of cause-effect linkages (causal links) which is intended to capture how the variables interrelate.

Causal loop diagram

An origin or ending place of a flow that is outside the boundary of the system. Represents and input or output of the system that is inconsequential to its behavior of interest. In a population system, this might represent origin of the inflow of "birth rate" and destination of death rate that determine a "population" stock.

Cloud

Phenomenon that occurs when the stock serves as the basis for generating its own inflow, producing exponential growth. The behavior is also said to be self-reinforcing.

Compounding

A flow that moves a quantity of material between two distinct stocks so that the total amount of material in that part of the system is unchanged. There is only so much material and it is divided between the two stocks.

Conserved flow

Generally known as auxiliary variables. Usually represented in diagrams by circles. Do not accumulate flows and do not have memory, but rather are recalculated from scratch each time calculations are performed.

Converter

A type of stock that represents a space into which material flows and stays for a fixed amount of time, then exits. Whatever entered first will also exit first.

Conveyor

A surprising result of policies devised to remedy a problem. As troubles increase, efforts are intensified which actually worsen the problem.

Counterintuitive behavior

An equation-based simulation language for system dynamics modeling on MS computers.

DYNAMO

also known as a rate equation. It is a policy statement that determines how the levels are related to the decisions (rates).

Decision function

A phenomenon where the effect of one variable on another does not occur immediately. Result from decisions often requires a long period of time to be effective. Can result in overshoot or oscillation.

Delays

A process that checks for unit consistency in equations.

Dimensional analysis

Done to separate variables that do not have similar effects on system behavior.

Disaggregation

Length of time it takes an exponentially growing quantity to double in size.

Doubling time

A model that deals w/ relationships that varies w/ time

Dynamic model

A "laboratory replica" of a real organization that involves a production / distribution system. The players at each position make decisions about placing orders, and find from practice the problems that originate from traditional ways of thinking and interaction.

The Beer Game