Computer simulation

A computer simulation is a simulation, run on a single computer, or a network of computers, to reproduce behavior of a system. The simulation uses an abstract model (a computer model, or a computational model) to simulate the system. Computer simulations have become a useful part of mathematical modeling of many natural systems in physics (computational physics), astrophysics, climatology, chemistry and biology, human systems in economics, psychology, social science, and engineering. Simulation of a system is represented as the running of the system's model. It can be used to explore and gain new insights into new technology and to estimate the performance of systems too complex for analytical solutions.

Computer simulations vary from computer programs that run a few minutes to network-based groups of computers running for hours to ongoing simulations that run for days. The scale of events being simulated by computer simulations has far exceeded anything possible (or perhaps even imaginable) using traditional paper-and-pencil mathematical modeling. Over 10 years ago, a desert-battle simulation of one force invading another involved the modeling of 66,239 tanks, trucks and other vehicles on simulated terrain around Kuwait, using multiple supercomputers in the DoD High Performance Computer Modernization Program Other examples include a 1-billion-atom model of material deformation; a 2.64-million-atom model of the complex maker of protein in all organisms, a ribosome, in 2005; a complete simulation of the life cycle of Mycoplasma genitalium in 2012; and the Blue Brain project at EPFL (Switzerland), begun in May 2005 to create the first computer simulation of the entire human brain, right down to the molecular level.

Rail transport modelling

Railway modelling (UK, Australia and Ireland) or model railroading (US and Canada) is a hobby in which rail transport systems are modelled at a reduced scale.

The scale models include locomotives, rolling stock, streetcars, tracks, signalling and landscapes including: countryside, roads, buildings, vehicles, model figures, lights, and features such as rivers, hills, and canyons.

The earliest model railways were the 'carpet railways' in the 1840s. Electric trains appeared around the start of the 20th century, but these were crude likenesses. Model trains today are more realistic. Today modelers create model railroad layouts, often recreating real locations and periods throughout history.

General description

Involvement ranges from possession of a train set to spending hours and large sums of money on a large and exacting model of a railroad and the scenery through which it passes, called a "layout". Hobbyists, called "railway modellers" or "model railroaders", may maintain models large enough to ride (see Live steam, Ridable miniature railway and Backyard railroad).