Bugs with Missing Data

[Marco2103-polimi]

Two issues have been identified when handling missing data.

First, the variable n_obs_ stored in all statistical models is not synchronized with the corrected value computed within the solver classes, which properly accounts for missing observations.

Second, the GCV numerator is computed as the sum over all the space-time locations (observed and not observed), while it should be only on the observed spatio-temporal locations.