[TRNSYS-users] DERIVATIVES/setNumericalDerivative/getNumericalSolution vs. roll your own

[Damian Birchler]

Hi there

Many of our in-house types as well as the few TESS types that I've looked at solve their ODEs internally, using a wide variety of methods from numerical to evaluating the explicit solution directly.

I'm very unclear about the (dis-)advantages of doing that vs. using the TRNSYS built-in functionality of DERIVATIVES/setNumericalDerivative/getNumericalSolution. Is DERIVATIVES & friends just

  1.  A user-friendly utility that helps a type developer may use to solve their ODEs
  2.  The preferred way of solving ODEs for overall convergence reasons (by "overall" I mean system-wide; between all units)
  3.  ...for overall correctness reasons?

My question is "informed" by Wikipedia's page on DAEs: https://en.wikipedia.org/wiki/Differential-algebraic_system_of_equations.

After skimming through it, I was wondering what it means if (for the purpose of this discussion) the ODEs of all units within a simulation are hidden in the blackbox of their corresponding unit, then the system to TRNSYS' eyes is completely "algebraic"...

Are we developing are in-house types in a "wrong" way?

Cheers,
Damian
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20230331/ec543239/attachment.htm>