Search found 3804 matches
- Tue Aug 13, 2013 8:57 pm
- Forum: Vensim
- Topic: Optimisation Crash
- Replies: 6
- Views: 3347
Re: Optimisation Crash
Actually I see that you're using XP so I tried that and I can replicate the crash. It works fine on Win7 and Mac. Your model generates floating point errors in its base run. Resolving those (try a much smaller time step for one thing), plus adding parameter bounds, will solve the problem, though it ...
- Tue Aug 13, 2013 4:17 pm
- Forum: Vensim
- Topic: Is it possible to display equation comments on grahps?
- Replies: 2
- Views: 1860
Re: Is it possible to display equation comments on grahps?
I assume that you mean a Custom Graph, in which case I believe that the answer is no.
If you mean the model diagram, the comment and units appear when you hover over a variable with the cursor.
If you mean the model diagram, the comment and units appear when you hover over a variable with the cursor.
- Tue Aug 13, 2013 4:11 pm
- Forum: Vensim
- Topic: Optimisation Crash
- Replies: 6
- Views: 3347
Re: Optimisation Crash
This works fine for me on Win7 6.1c - I assume you're on a Mac though? I'll move it over and give that a try. One thing that would help quite a bit here is to put upper and lower bounds on all your variables. Even if you can't determine narrow limits a priori, searching from 0 to 1 billion is a lot ...
- Tue Aug 13, 2013 4:05 pm
- Forum: Vensim
- Topic: Vensim DSS compilation error
- Replies: 9
- Views: 6002
Re: Vensim DSS compilation error
This may be a matter of 32 vs 64 bit system file locations. You probably need to check the paths for the calls to the compiler & includes in your mdl.bat.
An upgrade to the current version of Vensim would almost surely solve your problem. 5.7 is six years old and predates Win7.
An upgrade to the current version of Vensim would almost surely solve your problem. 5.7 is six years old and predates Win7.
- Mon Aug 12, 2013 3:27 pm
- Forum: Vensim
- Topic: Optimisation Crash
- Replies: 6
- Views: 3347
Re: Optimisation Crash
We need to know a little more - can you post the model and your control files? Upgrading to 6.1 could help, though I don't recall any optimization specific bug fixes.
- Sun Aug 11, 2013 2:53 pm
- Forum: Vensim
- Topic: model check - variable not defined
- Replies: 4
- Views: 4189
Re: model check - variable not defined
If you write out the integral, it's stock = { flow*dt + initial stock So the flow has to have the same units as the stock, with a time unit in the denominator. Then the flow's time cancels with dt (TIME STEP). Lookups can have units, though typical practice is to make things dimensionless, which sup...
- Fri Aug 09, 2013 5:51 pm
- Forum: Vensim
- Topic: How to display subscript control panel in JAVA UI?
- Replies: 6
- Views: 3842
Re: How to display subscript control panel in JAVA UI?
I think we need to know a little more about what graphs you're displaying, and how, to answer this.
- Fri Aug 09, 2013 5:49 pm
- Forum: Vensim
- Topic: QUEUE FIFO with ALLOCATE BY PRIORITY
- Replies: 3
- Views: 3076
Re: QUEUE FIFO with ALLOCATE BY PRIORITY
5.0a is indeed ancient.
The LP_SOLVE functionality is in an external function library (see http://vensim.com/workbench/ ) so it could potentially be adapted to 5.0, but I doubt it makes sense to do that.
The LP_SOLVE functionality is in an external function library (see http://vensim.com/workbench/ ) so it could potentially be adapted to 5.0, but I doubt it makes sense to do that.
- Fri Aug 09, 2013 5:44 pm
- Forum: Vensim
- Topic: model check - variable not defined
- Replies: 4
- Views: 4189
Re: model check - variable not defined
First of all, I applaud your efforts to replicate a model from the lit. I do this quite a bit myself, and find that I learn a lot more about a model by hand coding it. If you look closely at the error message, it indicates that "change in cust.orient." is undefined - you have two instances...
- Wed Aug 07, 2013 2:18 pm
- Forum: Vensim
- Topic: Attaching Table between two Variables in the SD Model
- Replies: 1
- Views: 2385
Re: Attaching Table between two Variables in the SD Model
Is this what you're after? http://vensim.com/lookups-in-vensim/
Also, check Chapter 8 of the User Guide. http://www.vensim.com/documentation/usr08.htm
Also, check Chapter 8 of the User Guide. http://www.vensim.com/documentation/usr08.htm
- Mon Aug 05, 2013 6:34 pm
- Forum: Vensim
- Topic: Appropriate formula
- Replies: 1
- Views: 2665
Re: Appropriate formula
There are some drawbacks to using real data - it can be a lot of work, and it can add features to your model that distract from a simple understanding of its behavior. However, the benefits often outweigh the drawbacks. Using real data may help you to discover problems in the model or the data, and ...
- Mon Aug 05, 2013 6:29 pm
- Forum: Vensim
- Topic: How to determine appropriate number of iterations
- Replies: 2
- Views: 2145
Re: How to determine appropriate number of iterations
As the admin said, there's no real rule. Payoff sensitivity is useful for testing whether you've found the max/min, and how broad it is, but not for determining the iterations to get there. Whether you care to continue optimizing depends on your purpose. If you're doing policy optimization for a fir...
- Mon Jul 29, 2013 3:39 pm
- Forum: Vensim
- Topic: Global scope constants (or variables)
- Replies: 5
- Views: 3204
Re: Global scope constants (or variables)
Two other notes: In DSS, rather than creating a constant and hiding it, you could create a :MACRO: to contain the constant. In this particular case, feps isn't really needed - you could use the ZIDZ function in place of the (x+feps) construction. If you want some behavior other than ZIDZ, you could ...
- Fri Jul 19, 2013 2:20 pm
- Forum: Vensim
- Topic: Waiting times in a doctor's surgery
- Replies: 21
- Views: 11240
Re: Waiting times in a doctor's surgery
I don't have it in front of me (traveling) but I think you're correct - my mistake.
- Fri Jul 19, 2013 2:17 pm
- Forum: Vensim
- Topic: time deley
- Replies: 12
- Views: 7827
Re: time deley
A time step lag in state updates is a pretty fundamental property of ODE systems, not to mention real physical systems. What are you trying to model that requires cascading instantaneous updates?
- Fri Jul 19, 2013 2:10 pm
- Forum: Vensim
- Topic: QUEUE FIFO with ALLOCATE BY PRIORITY
- Replies: 3
- Views: 3076
Re: QUEUE FIFO with ALLOCATE BY PRIORITY
Not 100% sure I understand the question, but I think it's not practical to manipulate queue contents at the item or even time step slat level. Also, any input to an ALLOC has to be an array - the function can't look inside a queue, unless you first somehow select the queue elements into an array. Ev...
- Fri Jul 12, 2013 9:50 pm
- Forum: Vensim
- Topic: Waiting times in a doctor's surgery
- Replies: 21
- Views: 11240
Re: Waiting times in a doctor's surgery
More options:
Unfortunately, with the runup to the SD conference, I'm super busy so it's tough to keep up, but I'll try to respond to comments.- Fri Jul 12, 2013 9:05 pm
- Forum: Vensim
- Topic: Waiting times in a doctor's surgery
- Replies: 21
- Views: 11240
Re: Waiting times in a doctor's surgery
I'm not familiar with WITNESS, but if it's a discrete event simulator it might be more suitable for some problems. Generally, the dividing line is between tactical/operational control problems, where you really care about distributions and individual elements, and more strategic problems that blend ...
- Fri Jul 12, 2013 1:46 pm
- Forum: Vensim
- Topic: reading a value from a tabbed array
- Replies: 3
- Views: 2490
Re: reading a value from a tabbed array
reservoir.mdl Here's an alternate way to arrange things, using an array of lookups and VECTOR SELECT to choose the active series. Rather than a tabbed array, you'd supply an array of lookups (see the subscripted version of the GET...LOOKUPS example model in the help system). There are probably othe...
- Wed Jul 10, 2013 9:55 pm
- Forum: Vensim
- Topic: Value with two decimal marks
- Replies: 6
- Views: 5192
Re: Value with two decimal marks
I haven't had a chance to check the code, but I suspect what it's doing is essentially using the c %g format convention, which chooses between a direct decimal or scientific notation, whichever is shortest. http://www.cplusplus.com/reference/cstdio/printf/ . Whether you get 0.9973 or 4.621e9 will de...
- Wed Jul 10, 2013 2:08 am
- Forum: Vensim
- Topic: Units errors with Smooth functions
- Replies: 3
- Views: 3390
Re: Units errors with Smooth functions
Now that I think about it, I'm guessing that you've written, smoothed x = SMOOTH( x, 8 ) where 8 (or whatever) is the smoothing time. The problem is that Vensim doesn't know the units for 8, so it assumes dmnl. Make the 8 a parameter, which also exposes it to sensitivity analysis, and give it units ...
- Wed Jul 10, 2013 2:02 am
- Forum: Vensim
- Topic: Units errors with Smooth functions
- Replies: 3
- Views: 3390
Re: Units errors with Smooth functions
Can you post an example?
- Tue Jul 09, 2013 4:45 am
- Forum: Vensim
- Topic: how to turn of WARNINGS ?
- Replies: 5
- Views: 5276
Re: how to turn of WARNINGS ?
You could modify the equation to suppress the error. Two possibilities: 1. Add an extra point to the lookup, at FINAL TIME or beyond. It won't get used, but will prevent running out of bounds. 2. use MIN(Time, 9) rather than Time as the input to the lookup. You probably also want to make the "9...
- Tue Jul 09, 2013 4:23 am
- Forum: Vensim
- Topic: Simultaneous Equation On My Model
- Replies: 4
- Views: 3374
Re: Simultaneous Equation On My Model
One possibility is to regard price as a stock that adjusts in response to pressures from supply/demand balance.
- Tue Jul 09, 2013 4:22 am
- Forum: Vensim
- Topic: Waiting times in a doctor's surgery
- Replies: 21
- Views: 11240
Re: Waiting times in a doctor's surgery
I see what you mean. The long tail of the exponential distribution of servicing patients seems weird compared to intuition about the actual process. However, the solution, MIN(max patients seen,patients waiting), fails two other reality checks. First, if TIME STEP <> 1, it doesn't work; for continuo...