Wikipedia:Reference desk/Archives/Mathematics/2012 June 14#n in definition of Green.27s theorem

In the following identity, $\backslash int\backslash int\backslash int\_V\; \backslash phi\; div(grad(\backslash psi))\; +\; grad(\backslash phi)\; \backslash cdot\; grad(\backslash psi)dV\; =\; \backslash int\backslash int\_S\; \backslash phi\; \backslash frac\{\backslash partial\; \backslash psi\}\{\backslash partial\; n\}dS$, 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)