Fix warning of FlipCell
Providing correct input to flipcell cause this warning to be triggered:
trunk/pkg/dem/Shop_01.cpp:65 flipCell: Flipping cell needs det(Id+flip)=1, check your input.
Missing addition of identity matrix
Providing correct input to flipcell cause this warning to be triggered:
trunk/pkg/dem/Shop_01.cpp:65 flipCell: Flipping cell needs det(Id+flip)=1, check your input.
Missing addition of identity matrix