`inf` value handling in the iamc api

[meksor]

Currently, ixmp4 allows inf values to be added for IAMC datapoints. There seem to be problems with serializing these values to json via the web api and filtering by them.

1. Should inf values even be allowed?
2. If yes, how do we represent them in json and efficiently serialize?
3. How do we filter by them, how are they used in the databases?

[danielhuppmann]

My view is that this shouldn't be allowed. Our standard use case is that IAMC datapoints should represent real values.

The only use case that I can think of where such a situation may occur is when dividing by zero, e.g. when calculating an efficiency. In such a case, using None implicitly (ie. not defining the value at all in the database) is a better solution rather than making the code substantially more complex (also thinking about visualizing in an app, etc.).

[meksor]

Great, that makes it easy

[danielhuppmann]

But for the record, I still think we should also guard against inf in ixmp4 when adding datapoints - just to avoid that users bypass the nomenclature checks.