Search found 3815 matches
- Thu Nov 13, 2014 6:55 pm
- Forum: Vensim
- Topic: basic vensim computation issue 2
- Replies: 15
- Views: 28634
Re: basic vensim computation issue 2
Certainly I was flippant to call mathematica weird when it surely is different, and as the product of a lot of person years of smart mathematicians and computer scientists, my default assumption would be that it's generally very smart. However, error propagation is not free, so the question is wheth...
- Wed Nov 12, 2014 10:22 pm
- Forum: Vensim
- Topic: basic vensim computation issue
- Replies: 3
- Views: 3141
Re: basic vensim computation issue
I think the short answer is that 1/100 isn't precisely .01 in binary - it's 0.01000000000000000020816681711722. If you multiply 100*(1/100) the error is reversible, but if you sum 1/100 a hundred times, the error accumulates.
- Wed Nov 12, 2014 10:09 pm
- Forum: Vensim
- Topic: basic vensim computation issue 2
- Replies: 15
- Views: 28634
Re: basic vensim computation issue 2
To look deeper, I think we'd need the first few values from the mathematica version at full precision. It may be mathematica that's weird. For example, in python at skulpt.org: stock = 0.0 dt = 0.0625 while (stock < 1.0): stock = stock + dt*(1.0/100.0) print("%8f %.16f" % (dt,stock) ) yiel...
- Wed Nov 12, 2014 9:36 pm
- Forum: Vensim
- Topic: basic vensim computation issue 2
- Replies: 15
- Views: 28634
Re: basic vensim computation issue 2
In the first model, I would not expect sawtooth behavior, except by luck. The issue is not the time step, it's that the inflow of 1/100 does not have a precise binary representation. Therefore the equality test against 1 will usually fail, because the sum of 100 values of 1/100 is not 1. I changed t...
- Wed Nov 05, 2014 2:52 pm
- Forum: Vensim
- Topic: how to limit the number of simulation when optimizing
- Replies: 10
- Views: 11692
Re: how to limit the number of simulation when optimizing
I changed the lower limit, so that any nonzero value of SIMS_MAX is recognized. Version 6.3a (soon) will incorporate that.
- Mon Nov 03, 2014 9:51 pm
- Forum: Vensim
- Topic: converting vensim models to stella
- Replies: 1
- Views: 2133
Re: converting vensim models to stella
We're working on XMILE compatibility.
- Mon Nov 03, 2014 6:45 pm
- Forum: Vensim
- Topic: how to limit the number of simulation when optimizing
- Replies: 10
- Views: 11692
Re: how to limit the number of simulation when optimizing
There's a funny (weird, not ha ha) quirk in the code, in that max sim values <= 10 are ignored. So, if you set it to 11, it should work. You could also try lowering the PASS LIMIT to 1.
- Mon Nov 03, 2014 6:33 pm
- Forum: Vensim
- Topic: computer speed
- Replies: 22
- Views: 31590
Re: computer speed
It's a separately priced item (email us for a quote). However, it may not immediately help you - its multithreading supports server usage, but doesn't paralellize the opt/sensi algorithms.
- Mon Nov 03, 2014 3:38 pm
- Forum: Vensim
- Topic: computer speed
- Replies: 22
- Views: 31590
Re: computer speed
The advance in hardware performance is argueably only part of the reason software has gotten faster, the other side to it being algorithmic advances. To my knowledge, Ventity for example, will follow modern solver strategies and use a variable time step, loosely speaking making "bigger steps&q...
- Mon Nov 03, 2014 3:20 pm
- Forum: Vensim
- Topic: how to limit the number of simulation when optimizing
- Replies: 10
- Views: 11692
Re: how to limit the number of simulation when optimizing
I'll have to take a look at the code - I suspect that the limit only gets checked between passes, not at every single iteration, in order to avoid a lot of if-then testing when normally not needed.
- Sun Nov 02, 2014 2:27 pm
- Forum: Vensim
- Topic: computer speed
- Replies: 22
- Views: 31590
Re: computer speed
Some thoughts on model speed here: http://blog.metasd.com/2011/01/optimizing-vensim-models/ CPU speed hasn't improved that much with respect to what matters for Vensim, https://www.cpubenchmark.net/singleThread.html However, if your existing machine is not an i7 with a high clock speed (>3GHz), ther...
- Sun Nov 02, 2014 2:34 am
- Forum: Vensim
- Topic: Are there inconsistencies in the Vensim DLL ?
- Replies: 6
- Views: 8796
Re: Are there inconsistencies in the Vensim DLL ?
I think I've found the bug - should be OK in the next release.
- Fri Oct 31, 2014 7:25 pm
- Forum: Vensim
- Topic: Are there inconsistencies in the Vensim DLL ?
- Replies: 6
- Views: 8796
Re: Are there inconsistencies in the Vensim DLL ?
FWIW, with SHOWMACRO|1 I do get consistent behavior (showing "#modelFractionalRate>CONTINUOUSRATE#" from either end).
There is an inconsistency for SHOWMACRO|0 - for some reason it doesn't suppress the macro variable in the uses direction.
There is an inconsistency for SHOWMACRO|0 - for some reason it doesn't suppress the macro variable in the uses direction.
- Fri Oct 31, 2014 5:37 pm
- Forum: Vensim
- Topic: venext - FUNC_DESC
- Replies: 4
- Views: 4945
Re: venext - FUNC_DESC
Reorder your dimensions as x[Range2-element1,Range1] - it always iterates over the last dimensions first, so this should be the same as before.
- Thu Oct 30, 2014 3:12 pm
- Forum: Vensim
- Topic: Are there inconsistencies in the Vensim DLL ?
- Replies: 6
- Views: 8796
Re: Are there inconsistencies in the Vensim DLL ?
I'd try SHOWMACRO|1 - in the meantime I'll take a look in the debugger.
- Wed Oct 29, 2014 7:04 pm
- Forum: Vensim
- Topic: Variables Missing from View
- Replies: 8
- Views: 5525
Re: Variables Missing from View
NewModel_Oct27b-restore3.mdl NewModel_Oct15-Reorg.mdl The bad news: I still don't know why this happened. The good news: I was able to restore the diagram from the Oct_15 version. First, I edited to the 15 file to break up the large diagram into several chunks. Then, using a text editor, I copied t...
- Wed Oct 29, 2014 5:14 pm
- Forum: Vensim
- Topic: Are there inconsistencies in the Vensim DLL ?
- Replies: 6
- Views: 8796
Re: Are there inconsistencies in the Vensim DLL ?
You might try including an .ini file in the .vpm that you're feeding to the .dll, with Tools>Options>Settings>Show Macro Variables set. My first guess would be that it's set to Hide (which is the default), but the Uses call is forgetting to check the attribute. Otherwise I'll have to take a look in ...
- Wed Oct 29, 2014 5:10 pm
- Forum: Vensim
- Topic: Variables Missing from View
- Replies: 8
- Views: 5525
Re: Variables Missing from View
The 22b version looks corrupted as well. Only about 10-20% of the first Reservoir view loads. It's still not clear what the problem really is. The diagram is large, but I've seen bigger, so I don't think that's the issue. Generally, switching back and forth between text and sketch view can cause sma...
- Tue Oct 28, 2014 10:48 pm
- Forum: Vensim
- Topic: Variables Missing from View
- Replies: 8
- Views: 5525
Re: Variables Missing from View
I can see the problem, but not sure how it happened. Do you have any earlier versions, in which they're still present on the diagram, that we could compare?
- Tue Oct 28, 2014 10:41 pm
- Forum: Vensim
- Topic: Delay 1 behaviour
- Replies: 2
- Views: 2549
Re: Delay 1 behaviour
NobugToo.mdl Good question. The difference is in the initialization. See attached, to which I've added an instance of the DELAY1i function, which corresponds with your explicit structure. The simple DELAY1 function is initialized in equilibrium, so that the initial outflow equals the initial inflow...
- Fri Oct 24, 2014 12:34 pm
- Forum: Vensim
- Topic: Unable to complete graph
- Replies: 3
- Views: 2947
Re: Unable to complete graph
I can't replicate this - it works fine for me. Usually this kind of thing indicates a failure to find the dataset, or a bad/empty dataset. Where is the model file when you're _not_ running it in the Samples directory? You could try pinning your custom graph on the sketch as an I/O object, and see if...
- Tue Oct 21, 2014 3:59 pm
- Forum: Vensim
- Topic: Opening multiple Vensim models at the same time (Wondows 8)
- Replies: 6
- Views: 5129
Re: Opening multiple Vensim models at the same time (Wondows
You can open two instances of the application and run independently in those, but they won't have any connection.
- Tue Oct 21, 2014 3:54 pm
- Forum: Vensim
- Topic: Vensim PLE Silent Installation
- Replies: 1
- Views: 1953
Re: Vensim PLE Silent Installation
We don't generally permit this because it bypasses the license agreement, but if you're setting up a computer lab, contact us at vensim@vensim.com and we may be able to work it out.
- Mon Oct 20, 2014 4:01 pm
- Forum: Vensim
- Topic: Get Auxiliary Value At Specific Time
- Replies: 3
- Views: 2172
Re: Get Auxiliary Value At Specific Time
A small word of caution: A formulation that tests for Time = Value can fail unexpectedly due to roundoff error, especially when TIME STEP is not a power of 2. To protect against this, you can check against Value <= Time < Value + TIME STEP, or use the PULSE function with width TIME STEP as your even...
- Fri Oct 10, 2014 10:44 pm
- Forum: Vensim
- Topic: How can I use a model with database operations in java ?
- Replies: 10
- Views: 4223
Re: How can I use a model with database operations in java ?
Also, using "1" for the runname is theoretically OK, but potentially troublesome, because that means your vdf will be named 1.vdf, which might have side effects. Can't say as I don't do it.