The stationary convection–diffusion equation describes the steady-state behavior of a convective-diffusive system. In a steady state, ⁠ ∂ c / ∂ t ⁠ = 0, so the equation to solve becomes the second order equation: ∇ ∇ ⋅ ⋅ ( − − D ∇ ∇ c + v c ) = R .