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[cellml-discussion] Dimensional consistency and unitsconversions (was [Fwd: Re: ten Tusscher model])


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  • From: david.nickerson at nus.edu.sg (David Nickerson)
  • Subject: [cellml-discussion] Dimensional consistency and unitsconversions (was [Fwd: Re: ten Tusscher model])
  • Date: Fri, 20 Apr 2007 23:14:35 +0800
> going back to the following equation Andrew supplied:
>
> amount_Na [nmol] = 10^-6 [dimensionless] * conc_Na [nmol / L] *
> vol[microL]
>
> How do you make this more 'valid'? (it is already valid dimensionally
> and numerically).

but it is not consistent or valid dimensionally. The specification says
that tools are not required to look at the units within mathematics but
that units are required. Tools are not, however, restricted from making
use of the units and to hope that we're not wasting our time putting
them in you'd expect some tools at least to interpret the units inside
the math, in which case this equation becomes (at least the way I would
look at the equation)

amount_Na [nmol] = 10^-6 [dimensionless] * conc_Na [nmol / L] * vol [uL]
=> 10^-6 [] * conc_Na [nmol / L] * vol[(10^-6 L/uL)*uL]]
=> 10^-6 [] * conc_Na [nmol / L] * (10^-6*vol [L])
=> 10^-12 * (conc_Na) * (vol) [nmol]

which is presumably not what the author intended (unless I have messed
something up?). Whereas if the equation was specified as

amount_Na [nmol] = 10^-6 [L/uL] * conc_Na [nmol / L] * vol [uL]
=> 10^-6 * (conc_Na) * (vol) [nmol]

as expected. I think it is only this second equation that could be used
in both units processing and units ignoring tools to give a consistent
solution. Which is the original point of discussion, if I remember
correctly.

The problem seems to be that the specification can be interpreted in
such a way that the second form of the equation is first "simplified" to
the first form before the multiplication is done, which I feel is wrong
and needs to be clarified in the specification.


Andre.


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