Page 180 - DCAP601_SIMULATION_AND_MODELING

Simulation and Modelling

Notes Note that the term computer simulation is broader than computer modeling, which entails that all
aspects are being modeled in the computer representation. However, computer simulation also
includes generating inputs from simulated users to run actual computer software or equipment,
with only part of the system being modeled: an example would be flight simulators which can
run machines as well as actual flight software.

Computer simulations are used in many fields, counting science, technology, entertainment,
health care, and business planning and scheduling.
Computer simulation was developed hand-in-hand with the rapid growth of the computer,
following its first large-scale deployment during the Manhattan Project in World War II to
model the process of nuclear detonation. It was a simulation of 12 hard spheres using a Monte
Carlo algorithm. There are many different types of computer simulations; the common feature
they all share is the attempt to generate a sample of representative scenarios for a model in
which a complete enumeration of all possible states of the model would be prohibitive or
impossible. Computer models were initially used as a supplement for other arguments, but
their use later became rather widespread.

Notes Computer simulation is often used as an adjunct to, or substitution for, modeling
systems for which simple closed form analytic solutions are not possible.

Data Preparation

The external data requirements of simulations and models vary extensively. For some, the input
might be just a few numbers (for example, simulation of a waveform of AC electricity on a
wire), while others might require terabytes of information (such as weather and climate models).
Input sources also vary widely:
1. Sensors and other physical devices connected to the model;
2. Control surfaces used to direct the progress of the simulation in some way;

3. Current or Historical data entered by hand;
4. Values extracted as by-product from other processes;
5. Values output for the purpose by other simulations, models, or processes.
Lastly, the time at which data is available varies:

1. “invariant” data is often built into the model code, either because the value is truly
invariant (e.g. the value of ) or because the designers consider the value to be invariant
for all cases of interest;
2. data can entered into the simulation when it starts up, for example by reading one or more
files, or by reading data from a preprocessor;

3. data can be provided during the simulation run, for example by a sensor network;
Because of this variety, and that a lot of common elements exist between diverse simulation
systems, there are a large number of specialized simulation languages. The best-known of these
must be Simula (sometimes Simula-67, after the year 1967 when it was proposed). There are now
many others.

Systems accepting data from external sources must be very careful in significant what they are
receiving. While it is easy for computers to read in values from text or binary files, what is much

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