Ventana software support forum

Hi all I tried to implement a model which produces dynamically (ando so without using the direct mathematical expression) a gaussian curve with variable parameters. The model works pretty well but in some cases when the medium value is too high and the standard deviation is too low so that I get a n...

One way to generate an approximate Gaussian dynamically is to use a delay chain with a lot of levels. The SMOOTHN or DELAYN functions are convenient for this. A single level of a smooth or 1st order delay is an Exponential or Erlang(1) distribution. As you reach a large number, it converges to Gaus...

tomfid wrote:What's the real world explanation of what you're trying to accomplish here?

Hi
I really don't know... it is included in a bigger model from one of my students as his final project so he is still working on it...
Regards
LC

The expression for the Gaussian is incomplete. The full pdf is: 1/SQRT(2*pi)/sigma*EXP( (x-mu)^2/2/sigma^2 ) That partially reconciles the two. They still differ, but I don't understand the rationale for the DIFF version, so I can't really comment on that, except to point out that it doesn't work f...

Tony identified the problem as the integration method, which is correct. Here's why. Simplifying and translating a bit, you have: in = 60 out = fout = if( stock > desired stock, alpha*stock, 0) for alpha =.06 and stock=1000, alpha*stock=in=60. However, if stock = desired stock, out = 0. So, the onl...

Hi everybody
pliiiisss look at the attached model... I need to understand why the two gaussian curves (one obtained with a mathematical formula the other with a Vensim model) show such different values at their maximum (one is correctly at 1 the other at 0.008).
Best regards
Lorenzo

Sorry, I must have got this confused with another thread. Change the integration type to Euler instead of RK4. I'm not sure why things are not working out correctly with RK4, I'll look into it. Hi, thank you a lot... I changed and it seemingly (and strangely) works... any rational explanation? Lore...

I don't understand the problem here. What stock is going negative? I never wrote that there is a stock going negative... I only wrote that I find it surpising that a stock with an output flow greater that it's only input flow stays at a constant value and I asked for a possible (rational) reason .....

Hi
I posted a reply that has been cancelled... the reply stays in the following screenshot....
L.

Administrator wrote:What values are you using for Alpha? The level does not go negative for me.

Hi, thank you for your answer. I use values greater that 0.06 (the steady state value). The problem (according to me) is that S1 stay at a constant value even if out1 is greater that in1....
Loorenzo

Hi all I would like to know what is wrong with the attached model. If you run it it is in a steady state with the level at a constant value but if you increase a little bit the alpha value you get an output flow greter than the input flow with the level still at a constant value. If moreover you inc...

liizz wrote:Hi Tom,

Thanks for reply.

I have used the Horizontal and Vertical Divisions to adjust the axes of my graph. But it remains unchanged.

Thanks
Liizz

Post the model so we can try to help you....
Larry

Hi all, I want to calculate the Actual Completion Date. But, since these variables (completion date based on labour and time to meet schedule) are based on calculations. Is there some built-in functions whereby I can achieve this? I think the Actual Completion can be considered as a variable and I ...

Hi all, I have created a stock 'Tasks to Do' but when I try moving the Initial set of tasks, the'Completing tasks' remain unchanged.. Plz reply 2 me.. Im in despair. I am not able to see what i actually miss out in it Thanks Liizz Hi you should follow the links back form Completion Rate and underst...

liizz wrote:Hi,

Is it possible to copy the structure of a model and paste it in a fresh one?

Thanks
Liizz

It seems to me simpler if you use the Save as option of the program....
Cheers
Larry

Hi, Thanks. Of course I never expected you to design my model. I always ask for suggestion or advice before because I do not have a strong exposure in system dynamics and at times i'm uncertain about my point. Doing an introductory module on System Dynamics at the college will not make me a genius ...

Hi everybody
get a glance to the attached model, maybe this is the right solution, it seems to work well for any value of TIME STEP.
Cheers
Lorenzo

Hi everybody I use Vensim 5.11 PLE and I have problems with the RANDOM UNIFORM function. It seems to me that this function generates the same stream of random (??) data at each run of the model as you can see form the attached model. So I think I'm making some strange error of which I am not aware.....

It is possible to emulate the sample if true function in PLE. Joined the model in mdl and vpm format tthat demonstrates it and that can be read with the Vensim player, if you cannot run the .mdl model in PLE. Regards. JJ Hi JJ great!!! :lol: :lol: many thanks.... I download the models and try to un...

tomfid wrote:That helps. I'll see if I can create something.

What you really need to simplify the accounting is the SAMPLE IF TRUE function in Vensim Pro or DSS.

Unfortunately [for me] I use Vensim PLE...
Lorenzo

I'm finding it quite messy to create a structure that meets this spec, using only the functions in PLE. I can't think of real physical process that has precisely this behavior. What are we actually modeling here? Here it's one: a succession of groups, one idependent from the others, arriving at a s...

Are you looking for pulses of controllable width and height, at random times? That can be implemented with a stock structure - I could cook up a demo structure if that's what you're after. I'm looking for pulses with random height and width that repeat with a random generated period but within each...

I'd start by separating out the "RANDOM UNIFORM( minH , maxH, 0 )*PULSE TRAIN(start, 1 , 6, FINAL TIME )" into two separate variables. It's impossible to debug when you cannot see what values are being generated by the functions. RN = RANDOM UNIFORM( minH , maxH, 0 ) PT = PULSE TRAIN(star...

Can you post what you have done and explain what you need? I'm struggling to understand what you want to achieve. First of all thank you. This is the "culprit": RANDOM UNIFORM( minH , maxH, 0 )*PULSE TRAIN(start, 1 , 6, FINAL TIME ) and as an attacment you find the model where I want to u...

Have you tried using the RANDOM UNIFORM function to generate the numbers that you then feed to the pulse train? Hi, thank you for your answer... I tried but surely I made some mistakes somewhere. If I use RANDOM UNIFORM for the amplitude and the width is higher than TIME STEP I get random aplitudes...