Optimisation of a model

User: "Altair Forum User"
Altair Employee
Updated by Altair Forum User

Submitted by Enric on Wed, 05/25/2011 - 15:11 

I had a question regarding a model which I am trying to create: please note I am quite new to Vissim.

I am trying to model the level of a solute in the blood using a mass-transfer model. The model is defined by a number of compartments, with mass flow occurring between them and a number of integration functions, plus 'unknown' constants which define the rates of mass flows between compartments. To create the model I have guessed these “unknown” constants and now the model is up and running. What I want to do is to “optimise” these constants to produce a model where the blood level most closely matches real, measured, values.

Please could you give me some guidance on this. I have two initial questions:

Obviously there a variable called “time” which ticks upwards as the model progresses. How can I access this variable to display another variable at a set time point (to compare to my actual values). ie. An operator which would allow the following function: WHEN time=x1 seconds, THEN display variable X. When time=x2 seconds, THEN display variable X. If I could do this, then I could perform the most simple form of optimisation by comparing variables visually ! In addition, being able to do this would give me a set of readings at set time points which I could use for optimisation.

In my relatively simple model, which produces in the end a single output (solute concentration), how can I devise a system that optimises the solute concentration curve against actual measured levels that I have at discrete time points ? I am not sure if I should be using the Cost function here.

Any guidance on this would be appreciated- and thanks. I'm not after someone doing the model for me, its more that I'm still getting to grips with what functions are available for this.

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