Caleb C. Fast
Graduate Student,
Computational and Applied Mathematics
Rice University
6100 Main Street - MS 134
Houston, Texas 77005-1892

Email: calebfast at rice dot edu
Office: Duncan Hall 3066

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Research Interests
  • Operations Research
  • Graph Theory
  • Mathematical Programming
  • Optimization
  • The Traveling Salesman Problem
  • The P-median Problem
  • The Zero-Forcing Problem
  • NP-Hard Problems

The Traveling Salesman Problem:

The TSP is a common problem in the fields of combinatorial optimization, graph theory, and operations research. Quite simply, given a set of cities, the TSP asks for the shortest path that visits each city once and then returns to its starting point. For more information, see William Cook's TSP Page.

Many solutions techniques for the TSP rely on linear programming; however, when a problem with an integer valued solution, such as the TSP, is approximated by a linear program, the fractional parts of the approximate solution will cause some error. The largest possible ratio of the costs of the integral true solution to the fractional approximate solution is known as the integrality gap.

My research focuses on proving the 4/3 Conjecture for the TSP, which states that the integrality gap of the common linear relaxation of the problem is 4/3. My masters thesis focuses specifically on a specific type of TSP instance known as "fractional 2-matching instances."


The p-Median Problem:

The p-Median problem is a facilities location problem in which the number of facilities to be located is fixed. Like the TSP, the p-Median problem is NP-hard. My research focuses on finding valid inequalities and developing branch-decomposition based approximation algorithms. The motivating application for my study of this problem was the allocation of a fixed number of medical backpacks to locations in Malawi.