Search found 2567 matches

by tomfid
Fri Jun 14, 2019 12:15 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 162

Re: Initializing model

This would be in equilibrium if desired push rate = customer order rate. However, there's no feedback enforcing that. Either the push rate must be based on some long-term expectation that is responsive to demand, or the demand must be responsive to inventory (e.g., through discount pricing).
by tomfid
Fri Jun 14, 2019 12:13 pm
Forum: Vensim
Topic: housing Model
Replies: 6
Views: 73

Re: housing Model

Interest rates affect the buyer's mortgage payment, which affects affordability and therefore demand. They don't affect construction cost (unless you're considering financing during construction).
by tomfid
Thu Jun 13, 2019 4:50 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 162

Re: Initializing model

Attachment missing?
by tomfid
Mon Jun 10, 2019 3:48 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 162

Re: Initializing model

You could create something like a "desired push rate" which represents the material to be sent through the chain. Then you'd have to have some kind of flexible policy at the sales end, like pricing and promotion needed to ensure that sales are sufficient to keep inventory from piling up or running s...
by tomfid
Mon Jun 10, 2019 1:12 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 162

Re: Initializing model

I see what you're getting at, but in a push system, there still needs to be an expectation or forecast of sales that governs how much to push.
by tomfid
Sun Jun 09, 2019 10:07 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 162

Re: Initializing model

You have the same kind of problem in your Desired Production Start Rate - it adjusts for WIP, but absent a shortage of WIP, it won't produce anything.
by tomfid
Sun Jun 09, 2019 4:16 am
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 162

Re: Initializing model

I think you've forgotten a term in desired production - currently it only adjusts the inventory level. It also needs to replace inventory losses (sales, or in your case expected orders, I think).
by tomfid
Sun Jun 09, 2019 4:04 am
Forum: Vensim
Topic: aggregating values over time steps
Replies: 3
Views: 40

Re: aggregating values over time steps

Financial totals are lagged by a year in reality as well. In other words, 2019 results aren't available at 2019.0; they're only available at then end of the year. However, for display purposes, you can create an alternate time axis (using TIME BASE) that's shifted by a year, and use that for reporti...
by tomfid
Tue Jun 04, 2019 1:26 am
Forum: Vensim
Topic: Sensitivity run
Replies: 9
Views: 98

Re: Sensitivity run

I think what you'd have to do is make multiple copies of your control file (.vsc), each with a different random seed. Then use the command script to load each vsc and run_sensitivity in succession.
by tomfid
Mon Jun 03, 2019 4:01 pm
Forum: Vensim
Topic: Sensitivity run
Replies: 9
Views: 98

Re: Sensitivity run

You can script everything with a command script - see RUN_SENSITIVITY.

You can't interrupt a sensitivity run for viewing, but you could break the test into subsets.
by tomfid
Sun Jun 02, 2019 3:05 pm
Forum: Vensim
Topic: Distribution Help!!!
Replies: 2
Views: 40

Re: Distribution Help!!!

For any distribution, shift=0 & scale=1 gives you a standard version.
by tomfid
Sat Jun 01, 2019 12:40 am
Forum: Vensim
Topic: Importing time series data from a textfile
Replies: 5
Views: 77

Re: Importing time series data from a textfile

You reference the rows and columns with the same notation as if it were an Excel file.
by tomfid
Sat Jun 01, 2019 12:39 am
Forum: Vensim
Topic: Importing time series data from a textfile
Replies: 5
Views: 77

Re: Importing time series data from a textfile

Check the sample models in the help system. For ext files, the tab name field is used for the delimiter.
http://vensim.com/documentation/fn_get_direct_data.htm
by tomfid
Fri May 31, 2019 10:06 pm
Forum: Vensim
Topic: Replicate optimization
Replies: 14
Views: 156

Re: Replicate optimization

A couple more that should be replicable:

https://metasd.com/category/model-libra ... imization/
by tomfid
Fri May 31, 2019 10:03 pm
Forum: Vensim
Topic: Replicate optimization
Replies: 14
Views: 156

Re: Replicate optimization

This is a good one from the 2015 SD conference: Jalali, Mohammad with Armin Ashouri Rad, Oscar Herrera-Restrepo and Hui Zhang Information Diffusion through Social Networks: the Case of an Online Petition (Dana Meadows Award Winner) The supporting material includes the full model and a command script...
by tomfid
Fri May 31, 2019 10:01 pm
Forum: Vensim
Topic: Importing time series data from a textfile
Replies: 5
Views: 77

Re: Importing time series data from a textfile

GET VDF DATA is for retrieving a value from a Vensim dataset, not a text file. I think you want to use either the GET DIRECT DATA function, or import the dataset from text to VDF. GET VDF DATA is rarely needed.
by tomfid
Thu May 30, 2019 7:34 pm
Forum: Vensim
Topic: Replicate optimization
Replies: 14
Views: 156

Re: Replicate optimization

Are you looking for applications, or how-to-use?
by tomfid
Tue May 28, 2019 1:41 pm
Forum: Vensim
Topic: Initialize from last run?
Replies: 7
Views: 1172

Re: Initialize from last run?

My impression is that it's overly picky, but I'm not sure what the trigger is. We can take a look.

Writing a short cmd script to run the base and full sim is helpful, if you haven't already done it.
by tomfid
Sun May 26, 2019 3:55 pm
Forum: Vensim
Topic: Replicate optimization
Replies: 14
Views: 156

Re: Replicate optimization

Yes. You can also use MCMC for simulated annealing, but I always start with random multistart (use the RRandom variant).
by tomfid
Sun May 26, 2019 3:53 pm
Forum: Vensim
Topic: Graph Shortcuts
Replies: 4
Views: 85

Re: Graph Shortcuts

Right-click the graph tool and check Tool Options > Activate on Variable Selection. (However, once that's on, it gets in the way of other tasks.)
by tomfid
Sun May 26, 2019 3:51 pm
Forum: Vensim
Topic: Frechet & MonteCarlo
Replies: 2
Views: 61

Re: Frechet & MonteCarlo

Use the sensitivity control to generate a uniform random variable and transform that in another model variable, just as you would for a regular simulation.
by tomfid
Thu May 23, 2019 12:47 pm
Forum: Vensim
Topic: FORECAST
Replies: 10
Views: 141

Re: FORECAST

In cases like this, I typically do something like the following: last x time = GET DATA LAST TIME( x ) last x = SAMPLE IF TRUE( time = last x time, x, x ) trend x = TREND( x, horizon, init trend ) last trend x = SAMPLE IF TRUE( time = last x time, x, x ) forecast x = last x*(1+last trend x*MAX(0,tim...
by tomfid
Thu May 23, 2019 1:57 am
Forum: Vensim
Topic: Problem with installing Vensim PLE
Replies: 3
Views: 490

Re: Problem with installing Vensim PLE

It seems like a valid link from here. What error do you see?
by tomfid
Wed May 22, 2019 1:51 pm
Forum: Vensim
Topic: Replicate optimization
Replies: 14
Views: 156

Re: Replicate optimization

Order matters, though in a sense that's a bad sign - it means there are many optima and you haven't found the global max. Using the RRandom multiple start helps somewhat because it varies the search order.

The random seed for the optimizer is another factor.
by tomfid
Tue May 14, 2019 2:17 pm
Forum: Vensim
Topic: Running with Different Timesteps
Replies: 16
Views: 264

Re: Running with Different Timesteps

My inclination would be to ignore such details - just make every year 365.25 days.

Otherwise, you could create a schedule of leap years in a lookup.