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


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  • From: j.lawson at auckland.ac.nz (James Lawson)
  • Subject: [cellml-discussion] how to units make a difference to simulation
  • Date: Mon, 06 Aug 2007 11:40:17 +1200
Hi all,

Recently Catherine said that she had a model that was running but not
producing the right output. Instead of producing a train of spikes, it
was just producing some kind of curve flattening off at an asymptote.
Then when she changed some units on a relevant variable from
dimensionless to the right units, she got the nice spiking output.

As for myself, I've been looking at a model which has both a normal
version and a scaled/non-dimensionalized version. When I consulted him
about the output I was getting and which equations I should be using
from his paper, the model author suggested that I use the
non-dimensionalised set of equations, since the model describes a very
stiff problem, and as such, that is what the ND'd equations are there
for. Wheras before I was just getting curves that looked nothing like I
want, I am now getting trains of spikes.

I realise the first example might be slightly different from the first
(damn I am sick of people who don't know how to write English, the
Americans, that is, telling me I need a 'z' everywhere!) but...

The point/question I want to raise here, is how does PCEnv / other
simulators treat units? Is it possible that some of the models in the
repository simply don't run or produce the right outputs because of the
units? If so, this would be news to me! It would also be frustrating
given the number of times we have to guess or spend hours poring over
equations trying to work out the units of a variable.

Thanks,
James Lawson


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