Bob Eberlein and I have a "proto-alpha" version of the Molecules up on the
Web for free download (http://www.std.com/vensim/molecules.html).
A very brief paper and some documentation on molecules is also available at
the web site. (Ive included a paragraph description at the end of this
message for those who missed the discussion of Molecules on this email list).
The molecules as they stand are proving useful to us and to others.
Consequently, it seemed like a good idea to make them available now, even
though we plan to extend them and create additional documentation in the
coming months.
Molecules are language neutral. Eventually we hope to have a product that
will work with all of the major system dynamics environments
(iThink,DYNAMO,PowerSim,Vensim...). We regret that the "proto alpha version"
currently is limited to the PC version of Vensim. (Technically, the software
will work with the Mac version of Vensim, too; but the Web installer only
installs to PCs at the moment). If you do not have Vensim you can download
Vensim PLE for free (http://www.std.com/vensim) and this will work with the
molecules.
Again, we hope you find the molecules useful. Please contribute any comments
or additional molecules that all this inspires. Naturally, any molecules your
contribute will be added with proper attribution, etc. Send comments and
molecules to me at
JimHines@Interserv.Com
DESCRIPTION: Molecules are building-blocks for SD models. They are small
stock-and-flow structures that are solutions to little modeling problems.
Molecules have always been with our field: Smooths and delays qualify. In
addition there are structures for representing prices, productivity, etc.
Very experienced modelers carry in their heads a warehouse of molecules. We
are trying to make these moelcules explicit, easy to discuss, easy to
refine, and easy to access for experienced and inexperienced modelers alike.
Molecules are not to be confused with Archetypes which are complete dynamic
lessons, really best captured as loops or in words. Archetypes represent
system dynamics wisdom. In contrast, molecules represent modeling wisdom and
are best represented as stock and flow diagrams or equations. Finally,
"Generic Structures" is a blanket term that covers archetypes, molecules, and
even certain classic models such as Jay Forresters Market Growth as
Influenced By Capital Investment.
Regards,
Jim Hines
JimHines@Interserv.Com
LeapTec and MIT