Vensim - AbsoluteAstronomy.com

Simulation software

Simulation software is based on the process of modeling a real phenomenon with a set of mathematical formulas. It is, essentially, a program that allows the user to observe an operation through simulation without actually performing that operation...

made by Ventana Systems, Inc. (Harvard, Massachusetts

Massachusetts

The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...

). Its purpose is to help companies to find an optimal solution for various situations that need analysis and where it's necessary to find out all possible results of future implementation or decision.

Vensim is able to simulate dynamic behaviour of systems, that are impossible to analyze without appropriate simulation software

Simulation software

, because they are unpredictable due to many influences, feedback

Feedback

Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...

etc. It helps with causality loop

Causality loop

A causality loop can refer to the following:*A temporal causality loop, or predestination paradox, more commonly referred to as a causality loop, is a theoretical phenomenon, which is said to occur when a chain of cause-effect events is circular...

s identification and finding leverage points.

This software also provides some other dynamic functions like arrays, Monte Carlo sensitivity analysis, optimization, data handling, application interfaces and others. Simulated situations may come from different sectors such as economics, business, science, social sector, environment etc. Its current version is 5.10a.

History

To save time and effort, Ventana Systems decided to stop remaking an old software and started to create their own simulation language

Simulation language

A computer simulation language describes the operation of a simulation on a computer. There are two major types of simulation: continuous and discrete event though more modern languages can handle combinations. Most languages also have a graphical interface and at least simple statistical gathering...

called Vensim. It was initially a Pascal

Pascal (programming language)

Pascal is an influential imperative and procedural programming language, designed in 1968/9 and published in 1970 by Niklaus Wirth as a small and efficient language intended to encourage good programming practices using structured programming and data structuring.A derivative known as Object Pascal...

extension, as the models were made in Vensim and then translated to a Pascal program for execution.

In 1988 the Vensim language was refactored to use the C language
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

and X-Window graphical environment. Windows 3.0
Windows 3.0
Windows 3.0, a graphical environment, is the third major release of Microsoft Windows, and was released on 22 May 1990. It became the first widely successful version of Windows and a rival to Apple Macintosh and the Commodore Amiga on the GUI front...

provided Vensim with more publicity.
In 1991 Vensim version 1.50 was released with additional functionality for modelling dynamic systems.
Version 1.60 was released in 1993 (+ guide). This version had various configurations: Standard, Professional and DSS.
In 1994 there was an improved version 1.61 on demand of its users.
In 1995 Vensim was adjusted also for Macintosh
Macintosh
The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

, it already supported Monte Carlo
Monte Carlo
Monte Carlo is an administrative area of the Principality of Monaco....

sensitivity simulation and there was a Model reader for free.
In 1996 the free PLE (Personal Learning Edition) was released for beginners to learn with.
1997 there was a new version 3.0 with a new interface and new documentation, there was also DLL
Dynamic-link library
Dynamic-link library , or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems...

with a possibility of linking with languages C, C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...

, Visual Basic
Visual Basic
Visual Basic is the third-generation event-driven programming language and integrated development environment from Microsoft for its COM programming model...

, Delphi
Delphi
Delphi is both an archaeological site and a modern town in Greece on the south-western spur of Mount Parnassus in the valley of Phocis.In Greek mythology, Delphi was the site of the Delphic oracle, the most important oracle in the classical Greek world, and a major site for the worship of the god...

and some other. This version was available for Windows 95/NT, 3.1, Macintosh and Power Macintosh
Power Macintosh
Power Macintosh, later Power Mac, was a line of Apple Macintosh workstation-class personal computers based on various models of PowerPC microprocessors that were developed, marketed, and supported by Apple Inc. from March 1994 until August 2006. The first models were the Power Macintosh 6100,...

.
Vensim 4 was released in 1999 with a new interface, new sketch objects, data connections to spreadsheets and other improvements in arrays (subscripting), mechanics and graphics. A version called PLE Plus was also created.
In 2000, many new functions were added in versions 4.1 and 4.2.
2 years Vensim with SyntheSim was released. SyntheSim allowed for quick simulations with immediate results. Ventana Systems started to offer updates online.
In 2003 there was a version 5.1 with ODBC database support. In the same year version 5.2 was offered, it involved Reference Mode editing tool, 2 months later version 5.2a. was an improvement of the previous one with Reference Mode behaviour.
In 2004 came version 5.3 on the market with navigation capabilities and flexible Copy+Paste function. Version PLE got a new function – possibility of multiple views. Version 5.3a in the same year added in the abiity to global rename variables making updating portions of a sketch easier . Still in the same year there was a version of PLE 5.4 that supported input and output objects for creation of control panels and overriding behavior.
In 2005 version 5.5 was released. It could publish single models packages with all necessary files to send to other people.
Year 2006 brought version 5.6 that supported Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...

that allowed work with models in foreign languages.
In 2007 version 5.7 added unchangeable constants, vector select function and a possibility of rewrite of the optimizer to improve performance and controllability.
Then came versions 5.8 a, b and current release is 5.8.e. It can make compiled models and access external functions (in DSS).

Use

Vensim is made for identifying causal loops and finding leverage points, developing, analyzing and packaging dynamic feedback models.
Simulations can be made for areas like finance

Finance

"Finance" is often defined simply as the management of money or “funds” management Modern finance, however, is a family of business activity that includes the origination, marketing, and management of cash and money surrogates through a variety of capital accounts, instruments, and markets created...

, market

Market

A market is one of many varieties of systems, institutions, procedures, social relations and infrastructures whereby parties engage in exchange. While parties may exchange goods and services by barter, most markets rely on sellers offering their goods or services in exchange for money from buyers...

, life cycles, management

Management

Management in all business and organizational activities is the act of getting people together to accomplish desired goals and objectives using available resources efficiently and effectively...

, and biology functions.

Vensim environment

Survey of Vensim versions and their features

Vensim has several versions according to the user's level or character of needs. Vensim is still being developed, there are often new releases and updates with fixed problems. PLE will remain free for educational purposes. There is a Licence which is generally valid for all versions of Vensim.

Version	Price	Functions
Vensim PLE (= Personal Learning Edition)	for free	For beginners – basic training version for personal learning of making models of system dynamics. Functions: causality loops (including positive and negative feedback), stock and flow diagrams, causal tracing , graphs, multiple views, graphical sensitivity analysis Sensitivity analysis Sensitivity analysis is the study of how the variation in the output of a statistical model can be attributed to different variations in the inputs of the model. Put another way, it is a technique for systematically changing variables in a model to determine the effects of such changes.In any... (SyntheSim), Reality Check
Vensim PLE Plus	charge	functions of previous version + data connectivity, multiple views, Monte Carlo sensitivity simulations, game simulations, new model-user interface, importing spreadsheets to get data
Vensim Professional	charge	functions of previous version + suitable for large and mode complicated models => causal tracing ^TM, optimization and subscripting (arrays).
Vensim DSS	charge	the same like professional version + interface development tool for creating management flight simulators, external functions, macros, compiled simulations...
Vensim Runtime (discontinued => Model Reader includes its functions)	~~for free~~	~~the same like DSS just without a possibility of modification models~~
Vensim Model Reader	for free	for reading the models somebody has sent you, without need to install other Vensim software
Vensim Demonstration Program	for free	shows features of Vensim, examples of models etc.

Feature descriptions

Causal tracing :
To discover what things are causing other things to change. Looking in one direction, you can discover which variables cause a particular variable to change. Looking in the other direction, you can discover which variables are changed (or used) by a particular variable. The variable under study is called the "workbench variable." There is a tool for an overview called uses tree (tree diagram of causal loops – goes through them forward and backward) and loops analysis tool (list of causal feedbacks)
Multiple views :
For splitting complicated models into parts showed on separated pages.
Reality Check :
Allows the user to make statements about models and verify if they are true.
Monte Carlo Sensitivity Simulations :
Sensitivity testing involves changing your assumptions about the value of inputs to the model while performing multiple simulations, then examining the uncertainty in selected output variables. Vensim’s Monte Carlo simulations, also known as Multivariate Sensitivity Simulations, automates sensitivity testing. Output can be displayed as graphs with confidence bounds, individual simulation traces, or histograms. Latin Hypercube

Hypercube

In geometry, a hypercube is an n-dimensional analogue of a square and a cube . It is a closed, compact, convex figure whose 1-skeleton consists of groups of opposite parallel line segments aligned in each of the space's dimensions, perpendicular to each other and of the same length.An...

sampling is also supported for faster sensitivity testing.
Optimization :
Dynamic models are typical for their sensitivity to constants. If the user needs to find their suitable values, he sets data series and parameters that should be adjusted and Vensim automatically tries out all possible combinations and gives you the best match.
Subscripting (arrays) :
Often a piece of model structure will need to be repeated over and over again. For example, a retail store might be replicated for many different regions, or a factory production process might be repeated several times. One method for repeating structure is to create and debug one structure, then copy and replicate that structure as many times as needed. However, this can lead to complex diagrams and hard-wiring of constant values and number of structures. A better way to repeat structure is to use subscripts. A subscript is created and added to the one original structure, creating as many structures as there are subscript elements. Now numbers of structures and numerical values for all structures can easily be changed. Diagrams are also neater.
Compiled simulation :
To speed up simulation by compilation in C.
SyntheSim :
When using SyntheSim, the results of the simulation are graphically overlaid on the model.

Other useful functions and add-ins

highlighting of variables that include invalid equations
lookup functions (to determine your own functional relationship between two variables)
packaging of model to send to the others

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.