reading a value from a tabbed array

[ldecrist]

I’ve entered a tabbed array in vensim. (No problem here. I imitated the sample and VENSIM seems happy enough.)
How do I have the model read a value out of it and assign it to a variable? Based on other instantaneous states in the model, I want x to be the value in row 3 column 5 of the array for this time step in order to make further calculations. Later, row 2 column 1. I have a variable for desired row, and a variable for desired column (eg. r=2 and c=1 for row 2 column 1)

Background/project:

I’m using vensim to model rivers and reservoir systems, and I’m using lookups for things like “reservoir release for ecosystem health” that changes based on a weather classification (wet, dry, or normal) and the time of year (monthly). It would be a 3 row, 12 column matrix.

It is currently programmed in as 3 lookups with 12 values each (f_wet, f_dry, and f_normal),
a function defining the weather patterns,

weather classification =
IF THEN ELSE (cumulative rainfall<3, 1, // dry
IF THEN ELSE (cumulative rainfall<7, 2, // normal
3)) // wet

and then another if statement choosing the correct lookup and pulling the value based on month.

release for ecosystem health =
IF THEN ELSE (weather classification = 1, f_dry(month), IF THEN ELSE (weather classification =2, f_normal(month), f_wet(month)))

This setup works and has been running, but I’m now looking at weather in a higher resolution (more categories for rainfall), and at different sets of releases for different reservoirs, and the number of variables is getting out of hand. (f_verywet_reservoir1, f_verywet_reservoir2, etc.)

I’m envisoning one definition of weather classification and one function to count the month, plus one tabbed array for each reservoir to assign a value to that reservoir’s release.

Potentially something like
variable =
LOOKUP FUNCTION OF SOME KIND (name of tabbed array, row, column)
which in my case would become
reservoir 1 release for ecosystem health =
LOOKUP FUNCTION OF SOME KIND (reservoir 1 array, weather classification, month)

Am I completely misunderstanding the purpose of tabbed arrays? If not, how do I read the release out of the tabbed array?

Thanks in advance for your help!

[Administrator]

Unfortunately there is no in-built function, but I have added a model that allows you to do this.

You use SUM to loop over the elements in the array, and select the correct one.

[tomfid]

reservoir.mdl

(3.61 KiB) Downloaded 209 times

Here's an alternate way to arrange things, using an array of lookups and VECTOR SELECT to choose the active series. Rather than a tabbed array, you'd supply an array of lookups (see the subscripted version of the GET...LOOKUPS example model in the help system).

There are probably other ways to arrange things, using VECTOR ELM MAP for example.

[ldecrist]

I'm using the sum/loop solution.

Thanks!