Philosophical Transactions of the Royal Society of London. Series A. Mathematical, Physical and Engineering Sciences (Philos. Trans. R. Soc. Lond. Ser. A Math. Phys. Eng. Sci.) (20080101), 366, no.~1876, 2671-2684. ISSN: 1364-503X (print).eISSN: 1471-2962.