Set Coulomb friction
L.Tc = F
set Coulomb friction parameters to [F -F], for a symmetric
Coulomb friction model.
L.Tc = [FP FM]
set Coulomb friction to [FP FM], for an asymmetric
Coulomb friction model. FP>0 and FM<0.
[1] Robotics, Vision & Control, Chap 7, P. Corke, Springer 2011.