explicitly a PDE : ∂ ∂ f ∂ ∂ t + d r d t ⋅ ⋅ ∂ ∂ f ∂ ∂ r + d p d t ⋅ ⋅ ∂ ∂ f ∂ ∂ p = 0 , and adapted it to the case of a plasma, leading to the systems of equations shown below. Here f is a general distribution function of particles with momentum p at coordinates r and given time t. Note that the term d p d t is the force F acting on the particle.