= Strang splitting contraction for symmetric diffusion and skew advection
{title2=$\|e^{kA/2}e^{kB}e^{kA/2}\|_2\leq1$}
If real matrices satisfy $A^T=A\leq0$ and $B^T=-B$, then $e^{tA}$ is a contraction and $e^{tB}$ is an <orthogonal matrix> for $t\geq0$. Hence $\|e^{kA/2}e^{kB}e^{kA/2}\|_2\leq1$ for every $k\geq0$. The bound is independent of commutativity and gives unconditional stability for a <centered convection-diffusion semidiscretization> with homogeneous <Dirichlet boundary conditions>. It does not itself bound the mesh-dependent commutators that enter a time-error estimate.
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