Disappearing Elements

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luzi
Junior Member
Posts: 5
Joined: Thu Nov 05, 2020 9:20 am
Vensim version: DSS

Disappearing Elements

Post by luzi »

I have been working with Vensim PLE and DSS happily for several years now.

I am now working on a mission critical model.

And suddenly, I encounter seemingly non-deterministic behaviour of Vensim.

Suddenly, various elements start disappearing.

We had been working on a model (see attachment "model 1"). Everything was fine.

Then we expand it slightly (see attachment "model 2").

While the model was open in Vensim, everything seemed fine. Elements we added were visible, they interacted correctly, and formulas could be edited as usual.

But as soon as we save the model, close Vensim, and open the model again, elements (seemingly randomly) start disappearing from all views - but not from the model logic!

So the result is that we now have working next versions, but they are virtually not editable and maintainable anymore, because you can't see the model structure anymore.

I tried to look into the text files to see what's happening. I clearly see that the disappeared variables are still in the model (formulas etc.), but that they are not contained in the lower part of the text files where the display coordinates etc. seem to be set.

To review the issue, take the two models attached. In "model 1", you can see the "Market Share competition" construct about in the center of the model, on the left of the "Headcount" graph. That variable is the source for the "Market_Share" graph at the bottom.

Then in "model 2", the said "Market Share competition" construct is completely gone, but the graph still works, and the variable is still in the model logic.

What is happening here?

To be clear: this is just one tiny example. When I was working on the model, I had expanded way beyond this, and had also continued working on the "broken", half disappearing model. Everything is logically working fine, but as said, we are running into more and more problems. By now, we are even seeing variable types change in the same way (e.g. flow becomes auxiliary).

I am using Vensim DSS 9.1.0 x64 on Windows.
Attachments
model 2.mdl
model 2 with disappearing elements
(29.55 KiB) Downloaded 88 times
model 1.mdl
model 1 fine
(26.48 KiB) Downloaded 85 times
tomfid
Administrator
Posts: 3804
Joined: Wed May 24, 2006 4:54 am

Re: Disappearing Elements

Post by tomfid »

Not sure what's happening, as I have not observed anything like this, though I've been a heavy user recently.

However, here's one guess. "Market share competition" has a companion, "Market share competition 0", that would appear to have been created by a copy-paste (replicate) operation. Area selections generally include hidden elements, so if the modeler selected the area around the undesired _0 version, deleting with the delete key "remove from diagram" option, that would delete both variables from the diagram, leaving both in the model.

You can restore the missing items with the Existing Variable or Shadow Variable tools.

I don't really have a theory for what could be happening in other cases. Any chance people are using different versions of Vensim? The changes in equation ordering between these 2 files are extensive, as if one had been through a reform & clean operation.

On the other symptom, flows & auxiliaries really have the same equation type. The diagram distinction is whether flow pipes are connected or not. Flow pipes can get disconnected in some cases. For example, if you edit a stock equation, leaving out a flow variable, the pipe will be deleted when you accept the equation change. It's possible that there's some additional issue making this more frequent. I tend to use View>Traditional Sketch Style, so it's also possible there's something I haven't seen. I'll switch and experiment.
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