Hi,

I'm working on a model for wastewater flows in a textile factory.

It has measurement data for flows, COD, non biodegradable COD and total nitrogen (TN).

__I find it hard to troubleshoot convergence issues with the model.__
Please see the attachment:

When only calculating individual layers (e.g. flow and COD) convergence is OK.

If I turn on all 4 layers for calculation, it won't converge (exceeds 100 steps).

The Trace Output does not give me any clues on where it is struggling to converge. Only saying: "calculation canceled after 100 iterations". The more detailed text messages are very cryptic and I can't see any warning or error there.

If I change the convergence tolerance in Calculation dialog to a large value like 5, the model does converge, fairly rapidly so.

On first inspection, most of the reconciled values are pretty good.

The Trace output however, now throws a large number of gross errors. Looking at those, most don't look to be gross errors. They have k-factors well below one.

__My questions:__
- how do the calculation settings influence convergence? (convergence tolerance, tolerance zero values and observable tolerance)

- is there extra info under the hood that can help in troubleshooting non convergence (pointing towards likely causes)?

- why are results with low k-factors flagged as gross errors?

Best regards,

Geert