Search found 2316 matches

by tomfid
Fri Aug 17, 2018 3:29 pm
Forum: Vensim
Topic: Legend modification
Replies: 1
Views: 7

Re: Legend modification

You can turn the legend off in a Custom Graph, or in the graph tool settings (right-click the tool and check "No Legend" under Appearance; not in PLE).
by tomfid
Fri Aug 17, 2018 1:57 pm
Forum: Vensim
Topic: Recover MDL file
Replies: 3
Views: 507

Re: Recover MDL file

What do you see in a text editor? Do you have the .2mdl backup file?
by tomfid
Thu Aug 16, 2018 1:21 pm
Forum: Ventity
Topic: bags in Ventity?
Replies: 8
Views: 27

Re: bags in Ventity?

PickNotExistNoDelete 1.zip This is an example. The trick is to use IsNull to check for an existing relationship in the Pick Vendor process list action. You can delete relationships, but then you can't subsequently resurrect one with the same key. This is something we're considering. There might be ...
by tomfid
Wed Aug 15, 2018 11:45 pm
Forum: Ventity
Topic: bags in Ventity?
Replies: 8
Views: 27

Re: bags in Ventity?

This can be done, as long as you don't need to delete relationships but reestablish them later. (There are probably workarounds if you do need that.)
by tomfid
Wed Aug 15, 2018 3:03 pm
Forum: Ventity
Topic: bags in Ventity?
Replies: 8
Views: 27

Re: bags in Ventity?

OK. So, the hard part is that firm is iterating over vendor[], but the check needed is for an instance of relationship[firm,vendor] where firm = the invoker and vendor = refVendor in the process list. I think it might be possible to construct a reference to the relationship populated that way, and u...
by tomfid
Wed Aug 15, 2018 2:21 pm
Forum: Ventity
Topic: bags in Ventity?
Replies: 8
Views: 27

Re: bags in Ventity?

Is this right?

You have
- firms
- vendors
- firm x vendor relationships

A firm iterates (process list) over the vendors for which there is not an existing firm x vendor relationship, picks n new vendors, and creates relationships with them.
by tomfid
Wed Aug 15, 2018 1:37 pm
Forum: Ventity
Topic: bags in Ventity?
Replies: 8
Views: 27

Re: bags in Ventity?

Does this selection happen at a single point in time, or does the state have to be remembered across time steps?
by tomfid
Tue Aug 14, 2018 2:24 pm
Forum: Vensim
Topic: warning of "ACTIVE INITIAL difference found"
Replies: 2
Views: 19

Re: warning of "ACTIVE INITIAL difference found"

This is explained in the help system here: https://www.vensim.com/documentation/ref_sim_errors.htm

This is probably just a usage of a RANDOM function that influences the initialization of a stock, perhaps in a macro like SMOOTH.

Probably nothing to worry about.
by tomfid
Mon Aug 13, 2018 3:03 pm
Forum: Ventity
Topic: Ventity 2.0 beta
Replies: 0
Views: 18

Ventity 2.0 beta

Ventity 2.0 beta, our most ambitious update yet, is here! In addition to a slew of bug fixes, we’ve also added several new key features (and a few improvements to already existing ones) that we’d like to take a moment to highlight. First up, to help with model creation and clarity we’ve added the dy...
by tomfid
Mon Aug 13, 2018 2:57 pm
Forum: Ventity
Topic: Ventity 1.3 Release
Replies: 3
Views: 200

Re: Ventity 1.3 Release

Ventity was indeed live on Forio at the conference!
by tomfid
Fri Aug 10, 2018 5:33 am
Forum: Vensim
Topic: How to determine equation ordering?
Replies: 3
Views: 39

Re: How to determine equation ordering?

Nice. I'd be interested to hear what ultimately works.
by tomfid
Thu Aug 09, 2018 7:18 am
Forum: Vensim
Topic: How to determine equation ordering?
Replies: 3
Views: 39

Re: How to determine equation ordering?

Right-click the document tool and change its settings to show All Equations, with Ordering: Comp.

I think PySD already does this, so check that first.
by tomfid
Wed Aug 01, 2018 4:02 pm
Forum: Vensim
Topic: optimize-calibration
Replies: 7
Views: 68

Re: optimize-calibration

35 parameters, or 35 variables in total?

If the model doesn't fit the data after you've extensively explored the parameter space, there are some generic possibilities:
- model structure is wrong or incomplete somehow
- data has systematic errors
- noise has moved the system state
by tomfid
Tue Jul 31, 2018 1:36 pm
Forum: Vensim
Topic: optimize-calibration
Replies: 7
Views: 68

Re: optimize-calibration

There's no difference, except with respect to Kalman Filtering. https://www.vensim.com/documentation/ref_kalman.htm
by tomfid
Mon Jul 30, 2018 4:38 pm
Forum: Ventity
Topic: Ventity 1.3 Release
Replies: 3
Views: 200

Re: Ventity 1.3 Release

We expect to be demonstrating it at the SD conference next week. I'm not sure when it'll really be commercially available on Forio, but I'd expect it to be very soon.
by tomfid
Thu Jul 26, 2018 2:49 am
Forum: Vensim
Topic: warm-up period
Replies: 5
Views: 56

Re: warm-up period

You can also use the "Resume" functionality to restart runs after a warmup run.
by tomfid
Thu Jul 26, 2018 2:49 am
Forum: Vensim
Topic: warm-up period
Replies: 5
Views: 56

Re: warm-up period

You can also use the "Resume" functionality to restart runs after a warmup run.
by tomfid
Wed Jul 18, 2018 11:07 am
Forum: Vensim
Topic: SD models for demand forcasting
Replies: 4
Views: 69

Re: SD models for demand forcasting

This is sort of relevant as an example: http://metasd.com/2013/11/facebook-reloaded-2013/
by tomfid
Wed Jul 18, 2018 11:02 am
Forum: Vensim
Topic: SD models for demand forcasting
Replies: 4
Views: 69

Re: SD models for demand forcasting

John Sterman's Business Dynamics has a whole chapter on this. However, this isn't really "demand forecasting" - it's inventory management. The demand forecast here is just a SMOOTH of sales. Forecasting sales requires a dynamic model of the behavior and physics of customers that causes sales. For ex...
by tomfid
Mon Jul 16, 2018 1:24 am
Forum: Vensim
Topic: Subscript error
Replies: 6
Views: 82

Re: Subscript error

I think the problem is exactly what the error message reports - you have different subscripts on the right and left side of the equation. "ps hydrostation small" vs. "ps hydrostation small group." That only works if you have one mapped to the other.
by tomfid
Fri Jul 13, 2018 3:33 am
Forum: Vensim
Topic: SD models for demand forcasting
Replies: 4
Views: 69

Re: SD models for demand forcasting

We do a ton of that, but the models are usually proprietary. http://www.ventanasystems.com/model_typ ... marketing/

"Demand forecasting" is a bit too broad to answer - demand for what? Over what horizon? For what purpose?

Have you searched the SD conference archives?
by tomfid
Thu Jul 12, 2018 1:08 pm
Forum: Vensim
Topic: sensitivity analysis
Replies: 2
Views: 49

Re: sensitivity analysis

I hadn't either, but I assume it refers to this: https://swat.tamu.edu/media/114860/usermanual_swatcup.pdf I'd probably have to go back to the source papers to find out what's really going on, but this discusses parameter ranges as if the problem were univariate. A key benefit of MCMC is that it gen...
by tomfid
Wed Jul 11, 2018 3:34 pm
Forum: Vensim
Topic: confidence bounds with MCMC
Replies: 8
Views: 98

Re: confidence bounds with MCMC

When the residuals are autocorrelated, the likelihood is wrong, because it assumes independence. This biases your confidence bounds; they'll be too narrow because it seems that you have more data than you really do. Global temperature is a good example - there are about 150 years of data, but there ...
by tomfid
Wed Jul 11, 2018 1:00 pm
Forum: Vensim
Topic: confidence bounds with MCMC
Replies: 8
Views: 98

Re: confidence bounds with MCMC

1 - right
2 - https://en.wikipedia.org/wiki/Durbin%E2 ... _statistic
3 - there are other, less complete ways, but nothing built in (this is something we're thinking about)
by tomfid
Tue Jul 10, 2018 9:28 pm
Forum: Vensim
Topic: confidence bounds with MCMC
Replies: 8
Views: 98

Re: confidence bounds with MCMC

MCMC always avoids any restrictions on the joint likelihood of the parameters, i.e. no ellipsoids. However, you can run into numerical problems if the likely volume is a low-dimensional manifold in a high-dimensional parameter space. This is not as rare as we'd hope. (Low acceptance rate could be a ...