Comparison to Other Approaches

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How is GoldSim Different from Other Simulation Software?

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Many special purpose simulators exist to simulate very specific types of systems. For example, tools exist for simulating the movement of water (and contaminants) in an estuary, the evolution of a galaxy, or the exchange rates for a set of currencies.  The key attribute of these tools is that they are highly specialized to solve a particular type of problem.  In many cases, these tools require great subject-matter expertise to use.  In other cases, however, the system being simulated may be so highly specified that using the tools is quite simple (i.e., the user is presented with a very limited number of options).

Other tools are not specialized to a particular type of problem.  Rather, they are "tool kits" or general purpose frameworks for simulating a wide variety of systems. There are are variety of such tools, each tailored for a specific type of problem.  What they all have in common, however, is that they allow the user to model how a system might evolve or change over time.  Such frameworks can be thought of as high-level programming languages that allow the user to simulate many different kinds of systems in a flexible way. We provide below a brief overview of how GoldSim differs from three of the most common types of general purpose simulation frameworks: discrete event simulatorssystem dynamics programs, and spreadsheets.

Discrete Event Simulators

Discrete simulators (such as ProModel, Arena, Extend, and Witness) generally rely on a transaction-flow approach to modeling systems. Models consist of entities (units of traffic), resources (elements that service entities), and control elements (elements that determine the states of the entities and resources). Discrete simulators are generally designed for simulating detailed processes such as call centers, factory operations, and shipping facilities.

GoldSim differs from most discrete simulators in the following manner:

  • GoldSim can simulate both discrete and continuous processes simultaneously. This is a distinct advantage when the system includes continuous flows or dynamics.
  • GoldSim was designed to build "top-down" models of complex systems that focus on "big picture" issues. As such, GoldSim is much better at simulating systems that have many diverse components that must be coupled together in a consistent manner in order to understand the behavior of the entire system (e.g., strategic business models, supply chains, portfolios of assets and/or projects, complex programs).
  • GoldSim is much better at simulating complex systems whose behavior is difficult to predict and/or poorly understood such that they have a high degree of uncertainty. Such systems include both natural systems (such as hydrological systems and ecosystems) and man-made systems (such as markets, businesses, and complex programs or development projects).
  • GoldSim is dimensionally aware and allows you to use any type of units without having to perform conversions or worry about unit errors.
  • GoldSim was designed to accommodate the addition of specialized extension modules, such as the Financial Module (for simulating financial instruments and processes), the Contaminant Transport Module (for simulating the fate and transport of chemical and radioactive constituents in the environment) and the Reliability Module (for simulating the reliability of complex engineered systems).
  • GoldSim is less effective at tracking detailed, carefully engineered systems whose interactions are precisely defined and controlled (such as assembly lines and call centers). If your system can best be described using a transaction-flow approach using only discrete events, a pure discrete event simulator would generally be a more appropriate tool than GoldSim.

System Dynamics

System dynamics software (such as Stella, iThink, Vensim, and Powersim) is based on the standard stock and flow approach developed by Professor Jay W. Forrester at MIT in the late 1950s and early 1960s. Models based on system dynamics are built using three principal element types (stocks, flows, and converters), and put emphasis on understanding the feedback structure of systems. System dynamics software packages are typically used for simulating business and organizational systems and simple engineering and scientific systems.

Although GoldSim is similar to system dynamics programs in many ways (and can simulate any kind of system that these tools can), GoldSim moves beyond the relatively restrictive stock and flow syntax in order to more realistically model complex systems. In particular, GoldSim differs from most system dynamics software packages by offering the following features:

  • GoldSim includes a much broader range of model objects (elements) that make the model logic and structure more transparent.
  • GoldSim provides powerful capabilities for superimposing the occurrence and consequences of discrete events (e.g., financial transactions, accidents, labor strikes, lawsuits) onto continuous systems.
  • GoldSim was specifically designed to quantitatively represent uncertain parameters and stochastic processes and events in the system. Because nearly all real-world systems are strongly influenced by such parameters, processes and events, predictive simulations must include a realistic representation of such system features.
  • GoldSim’s hierarchical submodel approach and other specialized programming features (e.g., local variables, looping/iterative submodels) allow you to build and efficiently maintain highly complex models (consisting of thousands of objects) without losing the ability to explain the models to a non-technical audience.
  • GoldSim is dimensionally aware and allows you to use any kind of units in your model. GoldSim checks for dimensional consistency and carries out the conversions for you automatically during model construction.
  • GoldSim was designed to accommodate the addition of specialized extension modules to realistically address systems that can not adequately be represented using the stock and flow paradigm.  This includes the Financial Module (for simulating financial instruments and associated stochastic processes), the Contaminant Transport Module (for simulating the coupled fate and transport of chemical and radioactive constituents in the environment) and the Reliability Module (for simulating the reliability of complex engineered systems).

You can download a short brochure describing key differences between GoldSim and system dynamics tools.

Spreadsheets (with Probabilistic Add-ins)

Spreadsheets are perhaps the simplest and most broadly used general purpose simulators. Although spreadsheets are inherently limited by their structure in many ways (e.g., representing complex dynamic processes is difficult, they cannot display the model structure graphically, and they require special add-ins to represent uncertainty), because of the ubiquity of spreadsheets, they are very widely used for simple simulation projects (particularly in the business world).

Probabilistic spreadsheet programs (such as @RISK and Crystal Ball) are add-in programs for Microsoft Excel that allow users to define probabilistic distributions for input parameters. Any type of system that can be represented in a spreadsheet can be simulated using probabilistic spreadsheet programs. One advantage of these programs compared with all other classes of simulation software is that most users are already familiar with spreadsheet programs.

GoldSim differs from probabilistic spreadsheet software in the following manner:

  • GoldSim is much better at simulating dynamic systems that evolve with time.
  • GoldSim’s graphical user interface makes it much easier to understand, demonstrate, and document the model logic and structure.
  • Although GoldSim’s object-oriented graphical interface is better for showing model logic, spreadsheets are better suited for rapidly assembling large amounts of data and calculations in a single view.
  • GoldSim’s hierarchical submodel approach allows simulation of highly complex systems without losing the ability to understand and explain the model. In other words, any spreadsheet model that involves multiple worksheets is probably easier to understand and explain using GoldSim.
  • GoldSim is dimensionally aware and allows you to use any kind of units in your model. GoldSim checks for dimensional consistency and carries out the conversions for you automatically.
  • GoldSim allows the user to build player files that can be viewed by anyone using GoldSim Player, a free download.
  • GoldSim was designed to accommodate the addition of specialized extension modules, such as the Financial Module (for simulating financial instruments and processes), the Contaminant Transport Module (for simulating the fate and transport of chemical and radioactive constituents in the environment) and the Reliability Module (for simulating the reliability of complex engineered systems).

A more detailed discussion of the advantages of GoldSim over spreadsheets can be found here.

Note that GoldSim supports seamless integration with existing spreadsheet models via a specialized element that allows the user to dynamically pass data to and from a spreadsheet during a simulation.

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Making Better Decisions In An Uncertain World