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

[Damian Birchler <damian.birchler@ost.ch>]

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