Search found 3816 matches
- Thu Feb 18, 2010 4:40 pm
- Forum: Vensim
- Topic: Allocate Available function
- Replies: 18
- Views: 9704
A basic assumption of the ALLOCATE logic, as I understand it, is that the quantities allocated are essentially an undifferentiated commodity. Given that the substitution relationships among resources are not symmetric, I think that assumption is violated. Therefore it does make sense to me to use a ...
- Thu Feb 18, 2010 2:08 am
- Forum: Vensim
- Topic: Optimization procedure
- Replies: 3
- Views: 2882
It sounds to me like you're actually asking about the objective function. In a calibration optimization, it is the sum of squared residuals, by whatever weights you select. (If you're using Kalman filtering, it's the log likelihood, more complex but same general idea). In a policy optimization, it's...
- Mon Feb 15, 2010 10:10 pm
- Forum: Vensim
- Topic: Subscripts and graphs.
- Replies: 4
- Views: 3227
As a rule, the left and right side have to have the same number of subscript ranges. They key here is that in example2[aircraft]=example1[aircraft,p1]+1 p1 is a single _element_ of probabilities, not a _range_. Therefore no corresponding range needs to exist on the left side. The left and right side...
- Mon Feb 15, 2010 8:56 pm
- Forum: Vensim
- Topic: about the utilization of the RC compare
- Replies: 3
- Views: 2829
- Mon Feb 15, 2010 8:54 pm
- Forum: Vensim
- Topic: Optimize Lookup
- Replies: 7
- Views: 4707
- Thu Jan 28, 2010 4:21 pm
- Forum: Vensim
- Topic: dowloading a model
- Replies: 2
- Views: 2470
There must be something funny about the server MIME types because the file downloads without an extension, so you need to add the .mdl to the file name. There appear to be other syntax errors as well. For example, land rent[land use type]= soybean land rent[Soybeans], corn land rent[Corn], ... needs...
- Thu Jan 28, 2010 5:17 am
- Forum: Vensim
- Topic: Allocation by priority
- Replies: 12
- Views: 11921
You can use ALLOCATE AVAILABLE with variables. The issue in the model posted on 1/15 is that attractiveness[Corn,pprofile]= 3,corn priority,0,0 ~~| mixes constants and auxiliaries. You need to reorganize your subscript equations, for example as: attractiveness[land use type,ptype] = land use ptype~~...
- Fri Jan 22, 2010 11:01 pm
- Forum: Vensim
- Topic: Accumulation
- Replies: 2
- Views: 2593
- Fri Jan 22, 2010 7:59 pm
- Forum: Vensim
- Topic: reiterate xls data
- Replies: 5
- Views: 3837
- Fri Jan 22, 2010 6:39 pm
- Forum: Vensim
- Topic: Vector lookup function
- Replies: 5
- Views: 4136
You can create a vector lookup using subscripts. It's not as convenient, but works. Here's one approach (not necessarily the best way to do the interpolation, but it works): interval weight[xNext]= MAX(0,MIN(1, (x input-x vals[xPrev])/(x vals[xNext]-x vals[xPrev]) )) ~~| interval weight[x1]= 1 ~ ~ |...
- Fri Jan 22, 2010 12:25 am
- Forum: System Dynamics Discussion
- Topic: statistical techniques and SD
- Replies: 4
- Views: 5143
Appropriate statistics for estimating dynamic models are described in Fred Schweppe's Uncertain Dynamic Systems , which is unfortunately out of print. David Peterson described the approach for SD in his thesis, http://dspace.mit.edu/handle/1721.1/27424 , which is more or less the basis of the implem...
- Fri Jan 22, 2010 12:12 am
- Forum: Vensim
- Topic: Allocation by priority
- Replies: 12
- Views: 11921
It may be possible to solve this problem using the FIND ZERO function to find a vector of prices that achieves some equilibrium condition. However, I agree with Bob that it would be better to be explicit about the dynamics. I would expect that you'd want stocks of land in each category - perhaps exp...
- Tue Oct 30, 2007 4:22 pm
- Forum: System Dynamics Discussion
- Topic: the math of delays
- Replies: 3
- Views: 4743
You might check out Chapter 5 of the Road Maps series, which includes 2 articles on delays. http://sysdyn.clexchange.org/road-maps/rm-toc.html
- Tue Sep 25, 2007 3:14 am
- Forum: System Dynamics Discussion
- Topic: System dynamicist
- Replies: 7
- Views: 6569
Originally posted by Monte Hi JJ, This definition might impress you: System dynamicist n. 1 a person who works in, or is skilled in the system dynamics technique. 2 a person who holds a Ph.D. degree in System Dynamics. People with a PHD are surely system dynamicists. Others who use SD effectively a...
- Wed May 24, 2006 1:56 pm
- Forum: Vensim
- Topic: World model
- Replies: 9
- Views: 6501
- Wed May 24, 2006 5:29 am
- Forum: Vensim
- Topic: World model
- Replies: 9
- Views: 6501
Hi JJ, Bob pointed out this thread to me. Based on a quick look at the 03 version, most of the out-of-bounds messages appear to be of little consequence, because they occur in places where the table function is already at a logical extreme or 0 slope anyway, so the default behavior is appropriate. T...