1. Center for the Study of Complex Systems, University of Michigan, Ann Arbor, MI 48109, USA, Department of Computer Science, University of Vermont, Burlington, VT 05404, USA and Vermont Complex Systems Center, University of Vermont, Burlington, VT 05404, USA
2. Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA and Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA
3. Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA and Center for the Study of Complex Systems, University of Michigan, Ann Arbor, MI 48109, USA