We are currently building a model where we would like some sections to run on an hourly basis, and others on a monthly or annual basis.
I have read the Vensim manual and online help, but couldn't get what I needed.
What does the manual mean when it says that variables should be 'marked' as using a particular time base? [extract below...]
thanks!
Puneeta
from manual:
-------------------------------------------------------------
Alternative Time Bases
Frequently, it is desirable to compute time on a monthly basis but survey model results on a yearly basis. In this case variables can be added to the list above to make the month-to-year conversion, and Vensim can be instructed to report results on a calendar (and/or fiscal) year basis, e.g.,
Decimal year = TIME BASE(INITIAL YEAR,YEARS PER MONTH)
~ year
~ decimal year date.
|
INITIAL YEAR = 1980
~ year
~ Start simulation on January 1, 1980.
|
YEARS PER MONTH = .083333
~ year/month
~ The number of years in a month.
|
When using different Time Bases, be careful to specify the basis on which data is entered. If data is on an annual basis and the model is in months an equation such as the one above must be included, and the data must be marked as using the time base Decimal year.
How do you implement differing time bases?
-
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Hello Puneeta,
>> We are currently building a model where we would like some sections
>> to run on an hourly basis, and others on a monthly or annual basis.
This may not be possible. The model will only run using one time step, to run different parts in different steps would need two models.
>> I have read the Vensim manual and online help, but couldn't get what I needed.
>> What does the manual mean when it says that variables should be 'marked'
>> as using a particular time base?
This is a way of changing the X axis on graphs so that it reads in years or days rather than months (for example). If the time line in the model is in months but some users want to see years on their graphs, you can use a "time base" to calculate the correct number of years and display this instead of the default.
So if your model ran in months, and a user wanted to see days on their graphs you would use
day time base=
TIME BASE ( initial day , days per month )
~ day
~ |
days per month=31
~ day/Month
~ |
initial day=0
~ day
~ |
To summarise, if you are after different graphical output then "time base" is what you need. If you want to run one part of the model in minutes and the other in days, you either need two models, or run the whole model in minutes and adjust output for those parameters you want on a daily basis.
Tony.
>> We are currently building a model where we would like some sections
>> to run on an hourly basis, and others on a monthly or annual basis.
This may not be possible. The model will only run using one time step, to run different parts in different steps would need two models.
>> I have read the Vensim manual and online help, but couldn't get what I needed.
>> What does the manual mean when it says that variables should be 'marked'
>> as using a particular time base?
This is a way of changing the X axis on graphs so that it reads in years or days rather than months (for example). If the time line in the model is in months but some users want to see years on their graphs, you can use a "time base" to calculate the correct number of years and display this instead of the default.
So if your model ran in months, and a user wanted to see days on their graphs you would use
day time base=
TIME BASE ( initial day , days per month )
~ day
~ |
days per month=31
~ day/Month
~ |
initial day=0
~ day
~ |
To summarise, if you are after different graphical output then "time base" is what you need. If you want to run one part of the model in minutes and the other in days, you either need two models, or run the whole model in minutes and adjust output for those parameters you want on a daily basis.
Tony.