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Unit 1: Introduction to System Simulation

and semantic constraints of some programming language. This program is the simulation model Notes
for the project. It is the execution of this program (or more correctly), Enhanced version of it; see
following and simulation project is an executable computer program that embodies the system
under investigation. The solution to the underlying problem is the simulation model for the
project. It is the execution of this program that is embedded in the project goal(s) is obtained
from the data reflected in this behaviour. As will the conceptual model. It evolves from a
transformation of a conceptual model and its simulation model and simulation appeared in
recent years; some examples are: SIMSCRIPT II.5, MODSIM, GPSS, SIMAN, ACSL, Modelica,
Arena, CSIM, and SIMPLE ++. Such languages generally provide features to support the
management of time, collection of data, and presentation of required output information. In the
case of projects in the DEDS domain, additional features for the generation of random variates,
management of queues, and the statistical analysis of data are also provided.
The simulation model is the penultimate stage of a development process that began with the
decision to formulate a modelling and simulation project to resolve an identified problem. The
Simulation model is a software product and as such, the process for its development shares
many of the general features that characterise the development of any software product.

Notes In the Figure 1.1 the transition from the conceptual model to the simulation model
is associated with two activities: namely, transformation and verification. As in the earlier
transition from project description to conceptual model, verification is required here to
confirm that the transformation has been correctly carried out.

Simulation Program

The outline of the simulation model provided above is idealised inasmuch as it suggests that the
simulation model is directly capable of providing the behaviour-generating mechanism for the
simulation activity. In reality this program code segment is never self-sufficient and a variety of
auxiliary services must be superimposed. The result of augmenting the simulation model with
complementary program infrastructure that provides these essential functional services is the
simulation program.
The services in question fall into two categories: one relates to fundamental implementation
issues whereas the other is very much dependent on the nature of the experiments that are
associated with the realisation of the project goals. Included within the first category are such
basic tasks as initialisation, control of the observation interval, management of stochastic features
(when present), solution of equations (e.g., the differential equations of a continuous system
model), data collection, and so on. Convenient programming constructs to deal with these
various tasks are normally provided in software environments specifically designed to support
the simulation activity. But this is certainly not the case in general-purpose programming
environments where considerable additional effort is often required to provide these functional
requirements.
The second category of functional services can include such features as data presentation (e.g.,
visualisation and animation), data analysis, database support, optimisation procedures, and the
like. The extent to which any particular modelling and simulation project requires services from
this second category can vary widely. Furthermore, modelling and simulation software
environments provide these services only to varying degrees and consequently, when they are
needed; care must be taken in choosing an environment that is able to deliver the required
services at an adequate level.

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