In theorem 4 of Approximability of Minimum-weight Cycle Covers Bodo Manthey proves that:
Then no approximation algorithm for $\operatorname{Min-L-DCC}$ achieves an approximation ratio of $o(n)$, where n is the number of vertices of the input graph.
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Thus, no recursive algorithm can achieve an approximation ratio of $o(n)$
Questions:
- is my conclusion right that there is general definition of approximation algorithms in the context of $NP$ completeness and that these algorithms are certain recursive algorithms that construct the solution for a problem with $n$ vertices from solutions for subsets of smaller size?
- Where can I find an exact definition of that class of approximation algorithms?