1. GLPK (GNU Linear Programming Kit). http://www.gnu.org/software/glpk/.
2. IBM ILOG CPLEX. http://www.ibm.com/software/integration/optimization/cplex-optimizer.
3. IPInfoDb. http://www.ipinfodb.com/index.php.
4. Y. Chon, N. Lane, Y. Kim, F. Zhao, and H. Cha. A large-scale study of mobile crowdsourcing with smartphones for urban sensing applications. In Proc. of ACM International Joint Conference on Pervasive and Ubiquitous Computing (UbiComp'13), Zurich, Switzerland, September 2013.
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