1. Center for Applied Mathematics, Cornell University, 657 Rhodes Hall, Ithaca, New York 14853, USA
2. School of Operations Research and Information Engineering, Center for Applied Mathematics, Cornell University, 228 Rhodes Hall, Ithaca, New York 14853, USA
3. Department of Mathematics, Sibley School of Mechanical and Aerospace Engineering, Cornell University, 417 Upson Hall, Ithaca, New York 14853, USA