@article{Blanes_2005,
title={On the necessity of negative coefficients for operator splitting schemes of order higher than two},
volume={54},
ISSN={0168-9274},
url={http://dx.doi.org/10.1016/j.apnum.2004.10.005},
DOI={10.1016/j.apnum.2004.10.005},
number={1},
journal={Applied Numerical Mathematics},
publisher={Elsevier BV},
author={Blanes,
Sergio and Casas,
Fernando},
year={2005},
month=jun,
pages={23–37} }