about testing Ventity beta release

[LAUJJL]

Hi

I have tried to test the first beta Ventity release, but quicky realised that Ventity at the present state is more like an empty cell compared to Vensim, and that if I want to compare really the capacity of Ventity compared to Vensim, I will have to compare both software for quite a while and regularly to be able to eventually decide to switch to Ventity. How long will it take ? Taking into consideration the time needed to test a new software, I have not the ressources in time to test on a continuous basis a software until it has reached a state that makes any serious comparison possible.

I prefer to regularly download the new beta releases, without testing them, until I feel that there are enough features that makes the comparison with Vensim possible.

I prefer to be frank about that fact and I have a doubt about the strategy of launching a beta that is at this low point of evolution. This strategy may still work, and if it works, all the better, forget what I said.

Best regards.

JJ

[tomfid]

Thanks for the straightforward feedback.

I think the right mindset is that Ventity is only preferred at the moment for problems where you need for one of its core language benefits:
- lists with arbitrary dimensionality of the members, as in a marketing mix model where one product has 7 packages, another has 12, etc.
- sparse matrices, like project prerequisites or an origin-destination table
- dynamic creation/deletion of structure, as in the cohort model

We're currently racing to implement enough functionality to do a commercial project, which requires time series data and calibration optimization. That means that a few other burning needs, like causal tracing, are a bit delayed, but they're coming.

Regardless of the timing, we really need user feedback as a guide, so please keep watching!

[LAUJJL]

Hi Tom

The only thing I would appreciate in Vensim, is reality checks that can be compiled, so as to run quickly, and be run in batch mode via DLL, so as to test models with an arbitrary set of parameter values.

What I appreciate in Vensim, is the possibility to group variables, so as to be able to erase them in text mode. I use this to split models in smaller parts to make them more manageable. I appreciate too the DLL capacities that I use mainly to run multiple automatic tests or make automatic analyses.
The same tests than RC but written in current Vensim language.

So far these possiblities are not yet implemented in Ventity.

Regards.

JJ

[tomfid]

Hi JJ -

Ventity may not ever have a text editor. You can use the inspectors for a list view of equations though, and it permits deletion.

In general, the modularity of entities is a lot better than the grouping in Vensim. You can, for example, reuse an entity in another model just by importing it. Also, entities have their own namespace, so you can have Price in your Fruit entity type and in your Vegetable entity type, without getting mixed up. We're weak on some other aspects of reuse, like copy-paste, but that will come.

We also intend to implement a second kind of hierarchical structure, more like the macros in Vensim, that permits collapsing structure into a module and (optionally) reusing it like a function.

There aren't any options for structure overrides, as in Reality Check tests and Synthesim, but our original spec did provide for a similar general capability for "alternate equations." This would allow you to treat equations like data, and change them the same way you would change constants via a .cin file. This would satisfy both the need to write idiosyncratic expressions for single entities (without getting bogged down in if-then logic) and permit Reality Check logic. At the moment other things are higher on the todo list though: causal tracing, interfaces, time series data and calibration, for example.

For parameter experiments, Ventity is already more powerful than Vensim in some ways. The Run Control lets you name multiple runs, using different data sets, that all execute when you hit the Run button. I'm finding that's a significant time saver in cases where I always want a Base run and a Policy run, for example.

[linear feedback]

"Ventity may not ever have a text editor. "

I hope this gets reconsidered. I did have a look at a smaller model and it is a pain to not have access to an overview in text form. Also, in Vensim the text editor is very useful for fast search&replace etc.

[tomfid]

Understood. There is an equation listing, though we haven't paid much attention to it lately. What if that were beefed up a bit, with editable entries and search & replace?

[linear feedback]

Sounds good to me. I can't judge really judge on this - gut feeling is the more the better in text form.

[LAUJJL]

Hi Tom

Will it be possible to run Vensim in batch mode with a full logic available in a procedural language like VBA in excel via the dll?

Regards.

JJ

[tomfid]

Yes - we haven't planned that piece yet, but we consider it to be important. We could potentially even support a similar syntax, though some things like arrays will have to differ. Is there anything in particular you'd like to see improved?

[LAUJJL]

Hi Tom

Up to now, I find Vensim very powerful and I do not see what else could be added apart making RC easier to use and possible to compile and run in batch as I explained.

The problem in SD when models reach a certain size is to make them tractable, well tested and easier to understand.

Everything that eases a top down building and testing of models must be improved. The possibility to split big models into smaller one easier to understand must be improved too.

To resume I personnally need more understanding than more power.

For instance I have ordered the new book about methods of building and analyzing SD models mainly based on Vensim.
But from what I expect, it develops sophisticated techniques that will eventually increase the power of SD, but not its applicability.

Best regards.

JJ