Consider the life of a traveling salesman: always on the move, a different client every day, trying to stay on schedule. Is there a retailing lesson to be learned from that experience? Wharton marketing researchers believe there is. They use a concept known as the “Traveling Salesman Problem” to study the behavior of grocery shoppers. The TSP, as it’s called in operations research, involves solving a fundamental question: If a salesman has to visit a number of cities, what is the shortest route he can take to cover all his stops and then return home? Grocery shoppers face the same challenge as they go about collecting milk, bread, cookies, or other things on their list, according to Wharton marketing professor Peter S. Fader .…