time unit

sintef · Post by **sintef** » Mon Nov 15, 2004 7:57 pm

I used powersim before, and the it can recognise the different time units, such as day, month and year, and transfer them automatically. Does vensim also has this function? I want to use yearly data mainly, but has some seasonal variation for some variables. How can I do this in vensim?

Post by **Administrator** » Tue Nov 16, 2004 9:08 am

The conversion between time units is not done automatically in Vensim. Data is kept seperatly from the model so always retains its original time unit.

If your model has a time step in months and your time series is in years, to convert it to months you just create a new aux variable which multiplies the data by "months per year". Make sure the dimensions for this parameter are "month/year", then when clicking the units checker, the model will be dimensionally correct.

Tony.

sintef · Post by **sintef** » Wed Nov 17, 2004 10:31 am

Thank you, Tony.

However, I don't understand your points very well. Could you please give me a simple example in vensim?

Post by **Administrator** » Wed Nov 17, 2004 1:45 pm

I can give an example, but I need a more specific question from you. Can you upload an example of the data you wish to use and what you want to do with it?

Tony.

sintef · Post by **sintef** » Wed Nov 17, 2004 3:06 pm

Hope you can understand what I mean in the attached file. I am really new to SD and Vensim.

Post by **Administrator** » Wed Nov 17, 2004 5:06 pm

Is the attached similar to what you are trying to do?

It is important to make use of the dimensional checker. Reference Demand is in MW/Year, and the multiplier "demand seasonal variation normal", I am not sure what units you want there (I assume it is just dimentionless). To convert "Demand" from MW/YEAR into something else needs more thinking about, but you should only need to divide by months/year or change the units on the multiplier, that is for you to decide as you are building the model.

I hope this makes sense. Basically I am just saying make sure you put in dimensions for all parameters, and click the check units button very often.

Tony.