Wikipedia:Reference desk/Archives/Mathematics/2012 June 14

= June 14 =

n in definition of Green's theorem
In the following identity, $$\int\int\int_V \phi div(grad(\psi)) + grad(\phi) \cdot grad(\psi)dV = \int\int_S \phi \frac{\partial \psi}{\partial n}dS$$, what does $$n$$ represent? ? Widener (talk) 20:40, 14 June 2012 (UTC)
 * It represents a normal -- this is the directional derivative in the direction perpendicular to the surface. Looie496 (talk) 21:18, 14 June 2012 (UTC)