Thus far we have been concentrating on exact solutions to problems which can be stated as integer programs. A major trouble we encounter is that since the time complexity of these problems is often at least O(2ⁿ), we cannot solve them for large inputs. Often when it is not feasible to compute an exact solution to a problem, we revert to approximation because this is better than no solution at all. These algorithms are often called heuristics since there is usually a rule of thumb at the core of the algorithm. But before examining heuristics in detail, we shall study several ways to analyze them.