H1 L3 interpolation inequality in three dimensions (source code)

= H1 L3 interpolation inequality in three dimensions
{c}
{title2=$\|u\|_3\leq C\|u\|_2^{1/2}\|u\|_{H^1}^{1/2}$}

On a bounded three-dimensional domain, interpolation between $L^2$ and the <Sobolev inequality> $H^1\hookrightarrow L^6$ gives
$$
\|u\|_{L^3}\leq C\|u\|_{L^2}^{1/2}\|u\|_{H^1}^{1/2}.
$$