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[cellml-discussion] CCGS changes


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  • From: david.nickerson at nus.edu.sg (David Nickerson)
  • Subject: [cellml-discussion] CCGS changes
  • Date: Mon, 30 Oct 2006 10:51:08 +0800
Great, thanks for the explanation Andrew.

> Hi Andre,
>
> There are two main changes:
> 1) The separation of code generation into two steps:
> a) generating a DAG of objects representing steps in a procedural
> process.
> b) DFS visit of the DAG, generating C code as a side effect.
> 2) Support for optimising numerical Jacobian calculations. This works by
> splitting the DAG visit into two steps: firstly visit starting from all
> equations used to compute variables directly used by the rate equations
> (so the DFS will catch all procedural steps needed to compute variables
> needed to compute the rates), and secondly (wrapped in #ifndef
> VARIABLES_FOR_RATES_ONLY) visits all remaining equations.
>
> Change 1 should not affect the output of the functions that get
> generated (it may change the ordering of assignments, but only to the
> extent that ordering does not matter, so you will still get the exact
> same results).
>
> Change 2 only makes any difference at all if you define
> VARIABLES_FOR_RATES_ONLY in your variableCodeFragment. Since this will
> not normally be defined, you don't have to do anything as a result of my
> changes.
>
> However, if you wanted, you could use my changes to get a more efficient
> Jacobian function, or to avoid computing variables that you don't need
> (if you define VARIABLES_FOR_RATES_ONLY, the code will not evaluate
> variables which do not directly affect the time evolution of your model.
> When computing the Jacobian, this is obviously a good idea, as it saves
> computing variables which will just be thrown away unused anyway. You
> might also want to do this for intermediate steps of the evaluation if
> you are going to look at the final result). The CIS utilises this by
> using variableCodeFragment twice, once with VARIABLES_FOR_RATES_ONLY
> defined, and once with it not defined.
>
> Best regards,
> Andrew
>
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--
David Nickerson, PhD
Research Fellow
Division of Bioengineering
Faculty of Engineering
National University of Singapore
Email: david.nickerson at nus.edu.sg


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