Consider the derivatives at boundaries in the 2D-table

[HansOlsson]

Issue: That is best described using the new test-model plot input and output of the derivative-blocks and see that the inputs don't change with time, but still half of them have spikes in their outputs (*).

Solution: If we are at boundaries between regions in the 2D-table we should ideally chose the branch we will be at in the future - or the one we were at in the past.

Detailed explanation:
For a 2D-table the problem is that we can be at a double boundary and the solution e.g., goes C->B, but in the middle we could select A or D, and in those regions the derivatives differ for linear interpolation.

A	B
C	D

This also explains why I ignored it for the 1D-tables; as we cannot be in such a point between four regions in a 1D-table.

*: All four variants now have the same issue. They didn't originally.

It might need a better explanation, better motivating example, and the actual code could be made less impactful.

[HansOlsson]

The example is now fully updated; and it turns out that there were more subtle differences for the cases.

The comment explains it:

• Case 2 and 4 slide diagonally (from different corners)
• Case 1 and 3 start at the edge of the real table and then leave it top-left - Interpolating in different ways

[HansOlsson]

Typo on line 505: /* Same as findRowIndex2 but works on rows */

should be /* Same as findRowIndex2 but works on columns */

Just to be clear: That is an existing issue, I just blindly copy-pasted. (But it is now corrected.)

ModelicaStandardLibrary/Modelica/Resources/C-Sources/ModelicaStandardTables.c

Line 497 in e5f0e7e

/* Same as findRowIndex but works on rows */

[beutlich]

@HansOlsson Will you rebase your branch to resolve the conficts or shall I?

[HansOlsson]

@HansOlsson Will you rebase your branch to resolve the conficts or shall I?

I can do it.

[beutlich]

@HansOlsson I added some minor formatting corrections and hope you agree on.

We should squash the commits anyway before/during the merge.

[beutlich]

@HansOlsson I added some missing cases (to have it fully symmetric between ModelicaStandardTables_CombiTable2D_getDerValue and ModelicaStandardTables_CombiTable2D_getDer2Value). Feel free to reset if you skipped these cases intentionally.

We should also squash all commits before the merge.

[HansOlsson]

@MartinOtter @sjoelund this PR has been stuck for about 2 months.