-Update_ExB_shear_flow asks a step num
-this step num can be set to -1 when used in control
-the sign have been checked
-coherent with Hamett et al.
-the NL factor comp. is not optmized but fully detailed
-still has issue to verify McMillan et al. test

-dirty (lots of uncommented lines)
-unoptimized (could remove aux var)
-ExB factor still not working

- not working yet

-1D routines development
-NL factor to correct moving grid method
-still an issue with the 1D r2c FFT
-ExB not working yet.

-it is made now in the increasing or decreasing kx order
-the order is decided with the sign of the jump (= sign of the ExBrate)