Three generalizations of the synthetic control method (which has
already an implementation in package 'Synth') are implemented: first,
'MSCMT' allows for using multiple outcome variables, second, time series
can be supplied as economic predictors, and third, a well-defined
cross-validation approach can be used.
Much effort has been taken to make the implementation as stable as possible
(including edge cases) without losing computational efficiency.
A detailed description of the main algorithms is given in
Becker and Klößner (2018)