eom_bounds

[Peter230655]

I just noticed this:
I wanted to bound the last eom, so I wrote eom_bounds = {-1: (a, b)}
I got an error: not enough degrees of freedom or similar.
Then I wrote (it is totally 9 eoms) : eom_bounds = {8: (a, b)} and all was fine.

My PR 490 should catch such a wrong key.
My question is this:
Since something like list[-1] is valid to get the last element of list, should we simply change such negative keys to correct ones with, say,
correct_key = len(eom) + negative_key

[moorepants]

The documentation does not say that a negative key works.

[Peter230655]

Fair enough.
The error message, however did not give a clou as the the real problem, the wrong key.
If PR 490 gets merged, then at least a useful error message will be given.