AN ABBREVIATED GLOSSARY OF SYSTEM TERMINOLOGY

Last Updated: 19 August 2001
 
 

A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z


-- A --

ADAPTIVE PROBING: A management device, characterized by exploration of diverse strategies, used to improve information about alternatives.

AGGREGATION: Lumping diverse objects together in a single category.

AMPLIFY: A system component or process that increases the magnitude of fluctuations or changes of a system variable. See DAMP.

ASYMPTOTE:

ASYMPTOTIC: An asymptotic function gradually approaches a constant value (the ASYMPTOTE); after some period time the function is arbitrarily close to the constant.

-- B --

BUDGET:

-- C --

CELLULAR AUTOMATA: Simplified mathematical models of spatial interactions, in which sites or cells on a landscape are assigned a particular state, which then changes stepwise according to specific rules conditioned on the states of neighboring cells.

CHANGE OF PHASE:

CHANGE OF STATE:

CHAOS: Complex dynamical behavior characterized by a lack of dominant periodicity and great sensitivity to initial conditions.

CLOSED SYSTEM:

COMPLEX ADAPTIVE SYSTEM:

COMPUTER MODEL (also called NUMERICAL MODEL): A construct of mathematical and logical statements that describe a complex system in quantitative terms with the help of a computer; a carefully constructed, but sharply limited simulation of nature in a computer. See also DEMONSTRATION, CONCEPTUAL MODEL.

CONCEPTUAL MODEL: A mental image of an object, system, or process.

CONSERVATION LAW: A statement describing a process wherein matter or energy or both are transformed, transported or stored without loss.

CONSERVATION OF ANGULAR MOMENTUM:

CONSERVATION OF MATTER: Matter may be neither created nor destroyed. A piece of matter may under go a CHANGE OF PHASE or may react chemically either within itself or with other matter, so it may not be recognizable in the same form, but the amount of matter does not change.

CONSERVATION OF ENERGY: Energy may be neither created nor destroyed. An amount of energy may under go a transformation or may be transported to another location, but the total amount of energy does not change. Within a CLOSED SYSTEM, energy may be transformed from one form to another, but the total amount cannot change. In an OPEN SYSTEM, there are exchanges of energy with the surrounding environment. During these exchanges, however, the change in total system energy must exactly equal the energy exchanged. Conservation of energy is the First Law Of Thermodynamics.

CONSTANT: A quantity that has a fixed mathematical value within a model, such as pi or the Earth's radius. It may appear explicitly in equations, logical statements, or as an initial value, or it may be a named parameter that the model uses.

CONSTRAINT: A restriction to the behavior of a variable. Constraints are similar to LIMITS, but usually act over a broader range of variable values.

CONTROLLED EXPERIMENT: A form of scientific investigation in which one variable, termed the independent or control variable, is manipulated to reveal the effect on another variable, termed the dependent or responding variable, while all other variables in the system are held fixed. See also SYSTEMATIC OBSERVATION, STATISTICAL EXPLANATION.

CONTROL(LED) VARIABLE:

CORRELATION: A statistical estimate of the relatedness of two events. See also UNCORRELATED.

CORRELATION LENGTH: The distance in space or the period in time beyond which events are UNCORRELATED.

COUPLED SYSTEMS: Two systems are coupled if information from one is provided to, and influences the behavior of, the other. The information being passed is termed the INTERCONNECTION.

CRITICALITY: The condition describing the transition between qualitatively different states, such as solid/liquid or liquid/gas.

CYBERNETIC: Relating to a control process.

CYCLE: A sequence of processes through which a system variable (or flow) ultimately returns to the reservoir from which it came. Sometimes called a closed loop in the system.

-- D --

DAMP: A system component or process that acts to decrease the extent of fluctuations or changes in a system variable is said to damp the variable. See AMPLIFY.

DATA: A group of facts, often in numerical form, describing the outcome of an experiment or the results of a systematic observations. Data are processed, filtered, analyzed, and interpreted to yield INFORMATION.

DEMONSTRATION: See also SIMULATION.

DISSIPATION:

DOUBLING TIME: The time required for a function or variable to increase its value by a factor of two.

DRIVER FUNCTION: See FORCING FUNCTION.

DYNAMIC EQUILIBRIUM: The state of system wherein the output continually changes but remains within fairly narrow bounds. The output is characterized by a mean value and a bounded range around that mean value. Example: water liquid in balance with the vapor, where the number of molecules leaving the liquid at any moment is approximately (but probably not exactly) equal to the number leaving the vapor for the liquid. But over any interval of time, these two quantities are equal. We say that condensation and evaporation are in dynamic equilibrium at saturation.

DYNAMIC PARAMETER: A value provided to a system that may change with time either in a prescribed manner or in response to the changing state of the system.

-- E --

e-FOLDING: An exponential function changes by the factor e or 1/e when the exponent of e changes by ~1.0. The time required for the exponent to change, or the distance over which it changes, by ~ is called, respectively, the e-folding time or the e-folding distance. See EXPONENTIAL.

ENERGY: The capacity to be active or to do work.

ENERGY BUDGET:

ENERGY CONSERVATION: See CONSERVATION OF ENERGY.

ENTHALPY:

ENTROPY: The scientific measure of the disorder in a system; the greater the disorder, the greater the entropy. See SECOND LAW OF THERMODYNAMICS.

EQUATION: A mathematical statement in which equal values (or the mathematical statements producing the values) appear to the right and left of an equal sign. In system modeling and programming, an equation is an action by which the left-hand side is set equal to the value produced by the evaluation of the right-hand side. The two sides are equal after the action is taken but may not have been equal prior to the action.

EQUILIBRIUM:

EVOLUTION:

EXPONENTIAL FUNCTION: A mathematical function, y = eax (here "a" is a CONSTANT and "e" is a constant equal to 2.718280), in which y asymptotically approaches 1.0 as ax approaches zero (i.e., for ax << 1.0) and y increases without an upper limit as ax increases far beyond 1.0 (i.e., for ax >> 1.0).

EXTERNAL FORCING:

-- F--

FEEDBACK: When information on a system's behavior is used by the system to modify its behavior, the process of transferring the information across the system is called feedback. This information is passed back through the system to the input via a feedback loop. Feedback loops can be tight (short, well defined, rapidly responding) or loose (long, ill-defined, slow responding).

A simple feedback system -- information from the Output is fed back and combined algebraically with the Input to control the flow into the Reservoir. With positive feedback (+), as the Output increases (decreases), the information passed back via the feedback loop is added to the Input, causing the inflow to the Reservoir to increase (decrease). With positive feedback, the modification of the Input is in the same direction as the behavior; in general, this leads to instability.

With negative feedback (-), as the Output increases (decreases), the information passed back via the feedback loop is subtracted from the Input, causing the inflow to the Reservoir to decrease (increase). With negative feedback, the modification of the Input is in the direction opposite to the behavior; in general, this constrains the system and leads to stability.
 
 

FIRST LAW OF THERMODYNAMICS:

FLOW: The movement of energy, material, or information from one place to another.

FLUX: The rate at which a variable enters or leaves a reservoir. As termed, a flow.

FLUCTUATION: Variations in the value of a variable, usually around the variable's locally averaged value.

FLUSHING RATE: The rate which liquids that enter a region are removed from it.

FORCED PROCESS:

FORCING FUNCTION: A parameter that controls the behavior of a system and makes its behavior regular and predictable. Also called the DRIVER FUNCTION.

FRACTAL: A self-similar structure whose geometrical and topographical features are recapitulated in miniature on finer and finer scales.

FUNCTION: A mathematical relationship between variables. See also FUNCTION in an ecological sense.

-- G --

GLOBAL SCALE:

-- H --

HEAT ENGINE: A mechanism that converts some of the energy present in a high temperature fluid into work. It is composed of four components:

A high-temperature energy source;

A working fluid;

A work to be done; and

A low-temperature energy sink.

HOMEOSTASIS: Regulation of a system property around a fixed set point.

HOMEORRHESIS: Regulation of system property around a changing set point.

-- I --

INFORMATION:

INITIAL CONDITIONS: The values assigned to all system variables at the "start time", the time or date when computations are to begin.

INSTABILITY:

INTERACTION: The relation among objects that do something to one another. Evidence of interaction is an observable effect that is interpreted as arising from the interaction of certain objects. For example, ocean tides on Earth are evidence of interaction between the Moon and ocean waters.

INTERCONNECTION: The information provided from one system to another, or from one part of a system to another part, that influences the behavior of the receiving system or part.

INTERFACE:

INTERNAL FORCING:

ISOLATED SYSTEM: A system that has no significant interactions with other systems or with the rest of the universe.

-- J --

-- K --
 
 

-- L --

LIFE CYCLE:

LIMITS:

LINEAR:

LINEAR SYSTEM:

LOCAL SCALE:

LOOP:

-- M --

MATTER:

MATTER CONSERVATION: See CONSERVATION OF MATTER.

MODEL:

-- N --

NEGATIVE FEEDBACK: Feedback that tends to counteract a process. See also POSITIVE FEEDBACK.

NEUTRAL EQUILIBRIUM:

NONLINEAR: Disproportionate in cause and effect.

NONLINEAR SYSTEM:

NORMAL DISTRIBUTION: A statistical distribution of a specific symmetric nature, representing the outcomes of a large number of basic random processes.

-- O --

OPEN SYSTEM:

OPTIMALITY: Condition of being best.

OPTIMIZATION: The search for the best solution among alternatives, or the extreme value of a variable or a function.

-- P --

PARAMETER:

PATH DEPENDENCY: The dependence of the outcome of a dynamical process on historical events.

PATTERN FORMATION: The emergence of large-scale patterns from local processes and interactions.

PERCOLATION: Mathematical theory of spread on cellular landscapes.

PERIODIC: Characterized by repetition of patterns in fixed intervals of space or time.

PHASE:

PHASE TRANSITION: Transformation of a substance or a system from one form to a qualitatively different one.

POSITIVE FEEDBACK: Feedback that tends to reinforce a process. See also NEGATIVE FEEDBACK.

POWER LAW: A relationship between two variables such that one is proportional to a power of the other.

PREDICTION: A statement foretelling the possible outcome(s) of an event, process, or experiment. In meteorology, a prediction is also called a forecast. A prediction is based on observations, experience, and scientific reasoning. A guess, on the other hand, is based on conjecture (speculation), chance, and intuition.

PRISONER'S DILEMA: A prototypical game theory problem involving two prisoners held in isolation; illustrative of the difficulties in achieving cooperative behavior.

PROCESS(ES)

PUMP:

-- Q --
 
 

-- R --
 
 

RECIPROCAL ALTRUISM: Mutually beneficial behavior in which an individual helps another because of expected reciprocal behavior.

RECOMBINATION: The genetic reshuffling of material with an organism due to the crossing over of chromosomes and reassortment of genes.

REDISTRIBUTION:

RELAXATION:

RESERVOIR:

RESIDENCE TIME: The average time an element of material spends in a reservoir; a characteristic time for a reservoir.

RESILENCY: The capability to resist qualitative shifts in behavior or characteristics.
 

-- S --

(TIME, SPACE) SCALE: Characteristic extent (in time or space).

SCHEMA (pl. SCHEMATA): Building block for discovering rules; an internal model of the real world.

SELF-ORGANIZATION: The development of macro-scale structure and functioning on the basis of local organization.

SELF-ORGANIZED CRITICALITY: The tendency of large complex systems to self-organize to a self-maintaining critical state.

SET POINT:

SIMPLEX METHOD: A method developed by George Bernard Dantzig for solving linear program problems.

SIMULATED ANNEALING: An optimization method that simulates the physical process of annealing by allowing the occasional acceptance of less attractive solutions or values.

SIMULATION: See also DEMONSTRATION.

SIMULATOR: A model -- physical or numerical -- that replicates some process. For example, SORTIE is a forest growth simulator developed by Stephen Pacala and his colleagues.

SINGULAR EVENT:

SINK:

SOURCE:

SPECIATION:

STABILITY: The tendency to return to normative behavior, such as an equilibrium or a limit cycle in a mathematical model.

STABLE EQUILIBRIUM:

STABLE STATE:

STATISTICAL EXPLANATION:

STATE:

STOCHASTIC: Governed by random chance, and so unpredictable.

STOCHASTIC CELLULAR AUTOMATA: Cellular automata in which rates are stochastic.

STOCHASTIC OPTIMIZATION: A class of mathematical optimization techniques that rely in part on the random generation of new variants of existing forms.

SUBSYSTEM: A system that is entirely included in another system.

SYSTEM: A group of related components or subsystems that form a whole. Systems are often selected because the components interact or have the ability to do so. Systems may be open or closed, linear or non-linear, stable or unstable.

SYSTEMATIC OBSERVATION:

SYSTEMS APPROACH:
 

-- T --

THERMODYNAMICS: Describes the "direction" of a process.

TIT FOR TAT: A strategy for cooperative behavior in which an individual, at each stage, plays the action last played by another against it.

TRANSFER PATH:

TRANSPORT: Any process wherein movement of matter and/or energy from one part of a system to another occurs. Energy moves with the matter being transported (latent heat transport in movement of water vapor) or separately (electromagnetic radiation). The movement of matter may be in bulk over global distances (ocean currents), or over regional or local lengths (turbulent mixing of stack emissions; diffusion of heat from surface).

TRAVELING SALESMAN PROBLEM: A classic problem in operations research; the objective is to find the shortest path a "traveling salesman" could follow in order to visit each of a set of geographically distributed locations.

TRIAGE: A system for allocating scarce resources; it provides the maximum resources to individuals of highest priority, and few or no resources to individuals of lowest priority. Derived from practices used to prevent medical systems from being overwhelmed when there are many sick or injured.

-- U --

UNCONTROLLED VARIABLE:

UNCORRELATED: Independent. See also CORRELATION.

UNSTABLE EQUILIBRIUM:

UNSTABLE STATE:

-- V --

VARIABLE: A condition that can differ from one experiment to another. Variables may be CONTROLLED or UNCONTROLLED.

VOTER MODEL: A particular form of interacting particle system in which every site (cell) is occupied by a specific type of particle, the identity of each particle changing with each iteration according to rules conditioned on the states of the neighboring cells.

-- W --

-- X --

-- Y --
 
 

-- Z --

ZONE OF TRANSITION: