Before revision:  Although many approximate/exact algorithms have been developed to solve this  problem on numerous properties, a solution obtained by these algorithms is often unsuitable for real-world applications due to the difficulty of building  mathematical models on real-world problems.
After revision:  Although many approximate/exact algorithms have been developed to solve this kind of problem on numerous properties, a solution obtained by these algorithms is often unsuitable for real-world applications due to the difficulty of building mathematical models on real-world problems.