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/// Education: Modeling and Simulation All Definitions (P – V)

Parallel Simulator
Distributed simulator whose goal is to speed up simulation of a model that could also be executed by a serial simulator. Parallelism is achieved through concurrent processing of tasks on individual processing units.

Parameter
Model variable that is set before a simulation run and does not change during the run. Its value may influence model behavior generated in the run.

Predictive Validity
Validity of a model with respect to a system within an experimental frame. Is affirmed if, given the system,
1.) It is possible to initialize the model to a state such that
2.) For the same input trajectory the model output trajectory predicts the system output trajectory within acceptable tolerance
Predictive validity is a stronger criterion than replicative validity

Replicative Validity
Validity is affirmed if, for all the experiments possible within the experimental frame, the trajectories and system agree within acceptable tolerance, usually in space or time, included in a model, the greater the included detail, the higher the level of resolution.

Scope
(Of a model) (Informal): the portion of a system the model is intended to represent, independent of the level of resolution that is used. Also called breadth of model. The greater the scope of a model, the higher its scope frame will be in the derivability partial ordering.

Scope Frame
(Of an experimental frame that is applicable to the model)
Every frame that is applicable to a model is derivable from its.

Simplification Procedure
Method or algorithm applied to a model to reduce its complexity while preserving its validity in an experimental frame, i.e., to achieve valid simplification

Simulation
Execution of a model by a simulator
Clarification:
The DIS glossary defines a simulation as a model (see DIS. simulation). In contrast, we sharply distinguish between the two concepts in any context in which a computer is essential. We consider computer simulation to be the process of generating behavior of a model using a simulator.

Simulation Run
An execution of a model by a simulator starting from an initial model state and generating a model trajectory

Simulator
Computer system (algorithm, single processor, or processor network) capable of executing a model to generate its behavior

Static Modeling Formalism
Modeling formalism capable only of expressing models that generate trajectories is structurally valid when its internal structure represents that of the system. Structural validity implies predictive validity implies replicative validity.

Structure
(Of a model) refers to the elements in a model as opposed to the behavior it generates. Think of the structure as what makes the model behave as it does

Synthetic Environment
A simulator capable of live simulation, constructive simulation and virtual simulation

System
System (or source system) Real or virtual environment viewed as a source of observational data or more specifically, behavior. This data is viewed or acquired through experimental frame of interest to the modeler. Model of the system are constructed in order to generate behavior that is indistinguishable from system behavior within one, or more, experimental frame.

Tolerance
(On trajectory comparison) (Informal) criterion for determining when two trajectories are accepted as being close enough to each other to be accepted as equal The tolerance is given as an interval where if the distance, as determined by a metric, between two trajectories falls within this interval they are accepted as equal

Trajectory
Time indexed data. A mapping of a time interval to the range set of a variable. It can be presented as a graphical plot of a variable against time

Valid Simplification
An operation on a model that both reduces its complexity and results in a homomorphism

Validity
Relation between a model, a system and an experimental frame. Answers the question of whether it is impossible to distinguish the model and system in the experimental frame.
In the most basic concept replicative validity, validity is affirmed if, as far as the experiments possible within the experimental frame, the behavior of the model and system agree within acceptable tolerance. Stronger forms of validity are predictive validity and structural validity.

Variable
(Of a model). Named slot that can be assigned a value from its associated range set

Verification
The process of verifying that the simulator of a model correctly generates its behavior

Virtual Simulation
Interactive simulation based on models with high realism