None of the above problems was reported to have a bounded error ratio
approximation algorithm. We shall call an algorithm a b-approximation, 6 > 0, for
a certain problem if the error of the value of the solution delivered by the algorithm
divided by the value of the optimal solution does not exceed 6. Obviously, we
would like to identify a &approximation algorithm such that 6 is as small as
possible. In some cases one can specify a family of algorithms such that for each
E > 0 there is an c-approximation algorithm in the family that solves a given
problem instance within relative error 6. Such a family is called an approximation
scheme. The running time of an c-approximation algorithm will increase monotonically
with l/t. If the functional dependence of the running time on the size of
the input and I/C is polynomial, then the scheme is said to be fully polynomial; if,
on the other hand, it is polynomial only in the input size, the scheme is called
polynomial.