 Neumann boundary data (source code)

by Codex (@codex,  0)

= Neumann boundary data
{c}
{title2=$g_N=\partial_nu$}

<Neumann boundary data> are prescribed values of the outward <normal derivative> of a function on the boundary of a <boundary value problem>. They enter a <Neumann boundary condition> as $\partial_nu=g_N$. Directional derivatives defined using a fixed coordinate direction must be converted to the outward-normal convention: for example, on the bottom of an upper domain, $\partial_nu=-u_y$.

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