to make the behavior in lightsim2grid and pandapower consistent in terms of the J matrix, we choose the "standard" vs "single slack" version of the solver bnased on the parameter "distributed_slack".
We transform the Ybus to csc if it is not yet csc. TODO for pandapower: define Ybus in csc in the first place if lightsim2grid is used (right now implemented via to_csc()).
+Some small changes