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[cellml-discussion] how to units make a difference to simulation


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  • From: alan.garny at dpag.ox.ac.uk (Alan Garny)
  • Subject: [cellml-discussion] how to units make a difference to simulation
  • Date: Tue, 7 Aug 2007 02:49:58 +0100
> As you know we (Catherine, you and I) spent a bit of time this morning
> trying to understand some models. One of the models that Catherine has
> been
> working on had problems with units. My understanding is that PCEnv
> didn't
> pick those problems up, while COR did. Correcting the problems,
> Catherine
> was able to get the model to "work" (I believe there might still be
> another
> problem, but not related to units this time).
>
> Anyway, the view we have now taken in Oxford is that models shouldn't
> have
> any problem related to units. This means that, dimensional
> equivalences,
> which are allowed in the CellML specification, are not "acceptable" to
> us.
> We should always have strict equivalences. E.g. A = B+C (with A and B
> in mV,
> while C in V) would be seen as being dimensionally equivalent and "OK"
> in
> regards to the CellML specification (and therefore COR, since it will
> only
> generate a warning). Yet, we would modify the equation so that it now
> reads:
> A = B+1000{millivolt_per_millivolt}*C. This may not be a great
> example, but
> I think you got the gist of it.
>
> The idea is, therefore, to have models that have no unit issues *at
> all*. I
> appreciate that this may seem a bit restrictive, but we have had so
> many
> issues with units over the years that we believe it will be worth it
> in the
> long term.
>
> Alternatively, we could have the software doing units conversion for
> the
> user... but that's another issue... and I understand that some are
> against
> that idea.

I have just realised that though the above might be an "acceptable" approach
for CellML 1.0 models, it might potentially be somewhat tricky to implement
for CellML 1.1 models... which makes me wonder whether we shouldn't be more
strict when it comes to units. At the end of the day, units are a very
common source of problems in model curation.

Alan.



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