From: Adaptive filters: stable but divergent
γ min(F)=
minΩRe{F(e jΩ)}
>0
minΩ{F(e jΩ)+F(e −jΩ)}
minx ≠0Re{x H F x}
minx ≠0{x H[F+F H]x}
mineig[F+F H]