REPLY The Minimum Acceptable Model Standard (SD6763)

[SDMAIL Jean-Jacques Laublé]

Posted by  Jean-Jacques Laublé <jean-jacques.lauble at wanadoo.fr>

Hi everybody

Concerning the possibility to read models from the conference, it seems that
even if it is possible to read models with Studio reader, the reader from Powersim does
not allow to look at the structure of the model, nor at the equations. It just runs
the model, and one is obliged to accept the results without the possibility to understand them.
'I think' is better for that, the downloadable no save version permits to
look at the structure and at the equations.
I do not know if the Vensim reader permits to look at the structure and the
equations, as I use a full Vensim version.
This means that the people who publish a model in Powersim, should publish
the structure of the model and a list of the equations with the units, to
allow for a full understanding of the model.

About the minimum acceptable conditions for a model, I have again browsed
the papers, and just verified if all the models available had units and
could stand units checking.
I did not verify all the papers, having not the time.

To my surprise, many of them have some minor errors (why not correct a minor
error?), some have more errors, and some have no units at all!!!
Only about 50% had no errors in units checking.

Before learning to run, one should first learn to creep.
Dimensional consistency is one of the basic check accepted by all authors,
that is mandatory to verify the conceptual consistency, that can be already used at the
qualitative CLD step of the modelling process (without having of course the
help of the software).

The dimensional consistency helps too to avoid bugs in equations and helps a
lot the external reader who wants to understand how the model works.
Some models have too warnings about the use of non dimensionless units in
lookup table.
It is not strictly a unit error, although lookup tables should be used with
ratio that generate a dimensionless unit variable as advised by many authors.

I did not try to make some mass conservation verification, but it would be
interesting if somebody could find the time to do it.

There are a lot of students, often making not very useful work.
They could perfectly verify the quality of the papers published in the
conference.

Just a question, what do the people who decide to accept the publication of
a paper, verify?

For example, after all my models, I verify in a separate view that all the
masses that can be verified (physical or not) are balanced.

Of course I do not speak about extreme conditions tests that are already too
sophisticated when compared to basic verifications.
Regards.
Jean-Jacques Laublé Eurli, Allocar
Strasbourg France.
Posted by  Jean-Jacques Laublé <jean-jacques.lauble at wanadoo.fr>
posting date  Wed, 20 Feb 2008 16:32:10 +0100