1. Department of Mathematics, Imperial College London, London SW7 2AZ, UK.
2. Institute of Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), Université Catholique de Louvain, Louvain-la-Neuve B-1348, Belgium.
3. Mathematical Institute, University of Oxford, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG, UK.
4. EPSRC Centre for Mathematics of Precision Healthcare, Imperial College London, London SW7 2AZ, UK.