Ventana software support forum

Apologies for the not-fully-clear question. I have attached an example now. My model starts in 1980, but my data starts in 2007. My time step is 0.125. How do I get the 'mortgages' variable to stay at zero when data in not available? I tried using the RAW setting for data import, but then it doesn't...

Hi, I was wondering whether there is a way to import data and have it return NA for empty cells, but still let it interpolate in between the data points (when the TIME STEP is smaller than the interval between data points). I guess this would be something in between the RAW and INTERPOLATE options. ...

Hi Tom, Thanks very much for your response. I agree with your instinct - I played around with it a bit, and using the continuous exponential discounting you suggested, the simulation replicates data sufficiently well. Just as a final follow-up, do you know of any references to cite off the top of yo...

..In other words, in formulas for monthly mortgage repayments what is multiplied by the discounting coefficient is P (the principal). However, modelling it in SD, if we use the "Stock of outstanding debt" instead of P, this means that payments get smaller over time as the stock gets deplet...

Hello, I wonder if I could ask this question once more: Thinking about formulating mortgage repayments, my model is at an aggregate level for the city of London, and I don't need to match any exact accounting data. However, I am still unsure whether I should formulate mortgage repayments like this: ...

Hi, I am building a model of London's long-term housing developments, and in part of my model I need to capture the effect of changes in house prices on new construction. Based on my review of the literature, an increase in house prices does not necessary lead to an increase in new construction, but...

Excellent. Thank you very much Tom!
Kaveh.

I think I am using Powell because the Optimizer is set to Powell by default and I am not changing it.

Hello, I am often using Vensim's automatic calibration for my PhD model. I am currently writing my Methodology chapter and I need a reference of some sort to cite when referring to the use of this automatic calibration function. Is there perhaps (if not a paper) an essay or a guide that I could cite...

Brilliant. Thanks for the super-quick response!

Hi, I was wondering whether Vensim has an automatic feature to generate a table/text output with all model constants and their values for documentation purposes. In my several years of using Vensim, I haven't seen such function but I just wanted to double check and also ask that, if not, is there a ...

Thank you both very much for your replies! I hadn't thought of continuous compounding which neatly resolves the unit inconsistency problem. Just to check I am implementing it correctly, the formula for mortgage repayments would then be: principal * (r/(1-EXP(-rt))) . Is that right? And if I may foll...

Hi Tom/colleagues, I am developing a small mortgage amortization model and I keep getting a unit error regarding the formulation of the mortgage repayment variable. My small model is attached, where I am using the following formula for calculating "monthly mortgage repayments": M = P [r * ...

Thanks Tom, I think I got the hang of it now.

Hi,

Is there any way to save a sensitivity graph as .vgd? (The reason I want to do this is to be able to edit it as text, in order to modify the x and y axis ranges)

Many thanks,
Kaveh.

Hi, I have some time-series data for prices and I would like to obtain its standard deviation over time as a measure of market volatility. In the attached model, I first try to obtain the moving average of the data, which I then use to get the standard deviation. However, the results that I get don'...

Hi,

Thanks very much for the reply.

The solution is simple and effective, thanks!
I think I could also use an IF THEN ELSE nested within the SMOOTH with two different delay times. Basically does the same.

Hi Tom/Colleagues, I am modelling a situation where changes in the backlog of unmet demand is affecting changes in prices. In this particular case, it seems that negative changes in demand backlog has proportionally stronger impact on prices than positive changes (possibly due to market 'panicking')...

Thank you Tom!

Thanks a lot for the quick reply!

Hi,

What is the best way to implement MIN (x, y, z) in Vensim. One can do MIN (x, MIN (y,z)), but this doesn't look very neat, especially if you have more than 3 alternatives.

Thank you.

Thanks a lot, Tom, for your prompt and helpful reply!

Hi,
Is it possible to have (add) more than 16 levels of depth?
I use the hide/unhide for presentation purposes, and for a sufficiently large sketch, 16 is not enough.
Thanks!

That's a good point. Unfortunately, our model is a huge one and this will not be an easy change. But something to think about...
Thanks anyway!

I know how to export changes (constants) into a CIN file and then load it in Sim Control to run a simulation based on it. However, what I would like to do further, is to actually incorporate those constant values into my model, so that the constant values in my current model actually change to those...