About the effective_pch_out_db of a ROADM

[Tobelightbeam]

Describe the bug
The propagate method of Class Roadm in gnpy.core.elements.py should be improved.

1. target_pch_out_db is used to calculate carriers_att. However, effective_pch_out_db (rather than target_pch_out_db) is used to update p_spani. The meanning of effective_pch_out_db is not clear.
2. As shown in the code, exceeding_att is introduced when carrier_power is lower than target_pch_out_db ( why not effective_pch_out_db?). In this case, it's reasonable to tunning the value of effective_pch_out_db accordingly. However, this step is missed.

p.s. The involved codes are between line 223 and line 243 in gnpy.core.elements.py

[EstherLerouzic]

I think this relates to another discussion we had on a proposed commit here: https://review.gerrithub.io/c/Telecominfraproject/oopt-gnpy/+/488967 (comments on sept. 04)
We have not finished on this discussion

[ojnas]

@Tobelightbeam, to clarify, the specific comment thread that @EstherLerouzic is referring to is this one:

https://review.gerrithub.io/c/Telecominfraproject/oopt-gnpy/+/488967/12/gnpy/core/elements.py#242

[Tobelightbeam]

@EstherLerouzic , @ojnas ,
Thanks for your replies.