robertm's blog
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enSysto - a lightweight approach for browser-based modelling
//www.simulistics.com/blog/systo-lightweight-approach-browser-based-modelling
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p><a href="http://www.systo.org">Systo</a> is a novel approach for supporting dynamic systems modelling in web pages.</p>
<p>Until recently, diagram-based modelling has required you to install software on your computer (like <a href="http://www.simulistics.com">Simile</a>, for example). Recently, developers have started producing browser-based apps which enable you to draw model diagrams, enter equations and values for the model, and run simulations. Examples for System Dynamics modelling are <a href="http://insightmaker.com/">InsightMaker</a> and <a href="https://sysdea.com/">Sysdea</a>. </p>
<p>In all these cases, the user is constrained by the particular design choices made by the developers - how things are laid out on the screen, and what functionality is provided. And yet, there is a lot in common - they all need to be able to show the model diagram, to provide a user interface for running simulations and displaying results, and so on. Wouldn't it be great if these various aspects could be packaged up as individual components ("widgets"), which others could then choose from and assemble in any way they wanted, customised for their own needs and those of their web page visitors?</p>
<p>That's what Systo enables you to do. Anybody who knows even very rudimentary HTML can put together a web page incorporating their choice of widget and models, for others to use. Some web pages might be very specific: presenting a single model with a tightly controlled user interface (i.e. set of widgets), while others might give the user a choice of models and/or a choice of widgets to be used in working with the models. People with some ability in Javascript programming can adapt, or develop from scratch, widgets, which can then be made available to anyone else. </p>
<p>If you would like to know more, and see Systo in action, please visit the Systo web page, at <a href="http://www.systo.org">http://www.systo.org</a>. Please be aware that, at the time of writing, things are very new, and liable to break or be changed in the coming weeks.</p>
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</div></div></div>Wed, 11 Sep 2013 14:52:50 +0000robertm4223 at //www.simulistics.com//www.simulistics.com/blog/systo-lightweight-approach-browser-based-modelling#commentsSystem Dynamics modelling in the Modelica modelling language
//www.simulistics.com/blog/system-dynamics-modelling-modelica-modelling-language
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>I've been looking at a number of other modelling languages, primarily to see how models are represented in the language. One of these is <a href="http://www.modelica.org">Modelica</a>, which is mainly aimed at the development of engineering-related models. A number of modelling environments, such as <a href="http://www.dynasim.se">Dymola</a>, are fully Modelica-compliant. </p>
<p>A typical Modelica model diagram contains symbols representing components such as electronic, hydraulic or mechanical components. For each domain, there is a Modelica library which contains not only the graphical definition of the symbol, but also its mathematical specification. This is represented in what is called an acausal manner - meaning that the inputs and outputs are not pre-defined. For example, a resistor is defined by the equation V = I.R, but a particular problem may require this equation be used to calculate R in terms of V and I. </p>
<p>This ability to define the mathematical nature of a symbol, and to do that in an acausal manner, is very elegant, but quite different from the approach typically used in biological/ecological/environmental modelling, which tends to use causal relationships (e.g. growth_rate = f(temperature) ), and to allow model builders to define the equations as they build the model.</p>
<p>One library is the <a href="http://www.modelica.org/libraries/SystemDynamics">System Dynamics library</a>. This defines symbols for standard System Dynamics elements, such as stock (level, compartment), flow etc. It was originally developed by Stefan Fabricius, but has been totally revised by <a href="http://www.inf.ethz.ch/personal/fcellier/">Francois Cellier</a>, at ETH (the Swiss Federal Institute of Technology) in Zurich. The library has been used to re-implement the Club of Rome World2 and World3 models, as described <a href="http://www.inf.ethz.ch/personal/fcellier/Pubs/World/modelica_08_world3.html">here</a>.</p>
<p>The attractive aspect of using Modelica for System Dynamics is that it is very straightforward to integrate System Dynamics models with those based on symbols from other domains, such as electronics and engineering. The downside, as I understand it, is that each different use of a System Dynamics symbol requires its own entry in the library. For example, a stock with one inflow and one outflow requires a different Modelica symbol from one with one inflow and 2 outflows. Also (again, as I understand it), every separate equation requires its own symbol to be defined and added to the library before it can be used. Both aspects represent a considerable limitation for the typical System Dynamics modeller, where both the diagramming and the equation entering are rather fluid aspects of the modelling process.</p>
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</div></div></div><div class="field field-name-taxonomyextra field-type-taxonomy-term-reference field-label-above"><div class="field-label">Taxonomy upgrade extras: </div><div class="field-items"><div class="field-item even"><a href="/category/tags/modelling-language">modelling language</a></div></div></div>Wed, 11 Feb 2009 11:05:16 +0000robertm1295 at //www.simulistics.com//www.simulistics.com/blog/system-dynamics-modelling-modelica-modelling-language#commentsDate-and-time for new forum topics and blog posts
//www.simulistics.com/blog/date-and-time-new-forum-topics-and-blog-posts
<div class="field field-name-body field-type-text-with-summary field-label-hidden"><div class="field-items"><div class="field-item even"><p>Can we add a date-and-time stamp to the list of 'New forum topics' and 'Recent blog posts' on the home page?</p>
</div></div></div>Thu, 06 Mar 2008 09:44:03 +0000robertm288 at //www.simulistics.com//www.simulistics.com/blog/date-and-time-new-forum-topics-and-blog-posts#comments