P-Complete Approximation Problems
Sartaj K. Sahni, Teofilo F. Gonzalez · Journal of the ACM · 1976
For P-complete problems such as traveling salesperson, cycle covers, 0-1 integer programming, multicommodity network flows, quadratic assignment, etc., it is shown that the approximation problem is also P-complete. In contrast with these results, a linear time approximation algorithm for the clustering problem is presented.