Question: what is one condition for diffusion to take place
Answer: For the diffusion equation , the no - flux boundary conditions can be formulated as ( J ( x ) , ν ( x ) ) = 0 ( \ displaystyle ( \ mathbf ( J ) ( x ) , \ nu ( x ) ) = 0 ) on the boundary , where ν ( \ displaystyle \ nu ) is the normal to the boundary at point x ( \ displaystyle x ) .