How does the approximate solution compare to the optimal solution?
An approximation algorithm has a ratio bound p(n) if for any input
of size n, the cost C of the approximate solution is within a factor p(n)
of the cost C* of the optimal solution:
where C/C* is used for minimization problems, and C*/C for maximization
Alternatively, an approximation algorithm has a relative error bound:
where (n) p(n) - 1.