Search found 2590 matches

by tomfid
Thu Jun 13, 2019 4:50 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 385

Re: Initializing model

Attachment missing?
by tomfid
Mon Jun 10, 2019 3:48 pm
Forum: Vensim
Topic: Initializing model
Replies: 14
Views: 385

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: 385

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: 385

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: 385

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: 106

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: 206

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: 206

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: 89

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: 160

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: 160

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: 300

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: 300

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: 160

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: 300

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: 1254

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: 300

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: 160

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: 121

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: 256

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: 562

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: 300

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: 418

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.
by tomfid
Tue May 14, 2019 1:38 pm
Forum: Vensim
Topic: Running with Different Timesteps
Replies: 16
Views: 418

Re: Running with Different Timesteps

Combining these, I think you want something like the following: crops.png Growth will be a continuous process, something like: Growth = Effect of Water Availability * Crops * Normal Growth Rate * (1 - Crops/Max Crops) Then Harvest is a discrete event: Harvest Trigger = PULSE TRAIN( ... ) Harvest = H...
by tomfid
Tue May 14, 2019 1:35 pm
Forum: Vensim
Topic: Running with Different Timesteps
Replies: 16
Views: 418

Re: Running with Different Timesteps

Two issues here: 1. I think the model would be clearer with more physical variable names and concepts. For example, "yield reduction" is not a thing. You want to model the physical state, which is - I think - the amount of crops in the field. 2. I'm not sure why TIME STEP is in the denominator for Y...