@article{Kro-Kun-Zid-2015,
    author={Axel Kröner and Karl Kunisch and Hasnaa Zidani },
    title={Optimal feedback control of undamped wave equations by solving 
           a HJB equation },
    doi={10.1051/cocv/2014033 },
    journal={ESAIM: Control, Optimisation, and Calculus of Variations },
    year={2015 },
    volume={21(2) },
    pages={442--464},
}