Assume that \(π(π)\) and \(π(π)\) are asymptotically positive. Which ofβ¦
2022
Assume thatΒ \(π(π)\)Β andΒ \(π(π)\)Β are asymptotically positive. Which of the following is correct ?
- A.
\(f(n)=O(g(n))\)Β andΒ\(g(n)=O(h(n)) \Rightarrow f(n)=\omega(h(n))\) - B.
\(f(n)=\Omega(g(n))\)Β andΒ\(g(n)=\Omega(h(n)) \Rightarrow f(n)=O(h(n))\) - C.
\(f(n)=o(g(n))\)Β andΒ\(g(n)=o(h(n)) \Rightarrow f(n)=o(h(n))\) - D.
\(f(n)=\omega(g(n))\)Β andΒ\(g(n)=\omega(h(n)) \Rightarrow f(n)=\Omega(h(n))\)
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Correct answer: C
Summary: determine which implications are true and give short justifications.
Statement "f(n)=O(g(n)) and g(n)=O(h(n)) β f(n)=Ο(h(n))": false. Counterexample: take f(n)=n, g(n)=n, h(n)=n. The premises hold but f(n)/h(n)=1, so f(n) is not Ο(h(n)). The correct conclusion is f(n)=O(h(n)).
Statement "f(n)=Ξ©(g(n)) and g(n)=Ξ©(h(n)) β f(n)=O(h(n))": false. From the premises you get f(n)=Ξ©(h(n)). Example: f(n)=n^2, g(n)=n, h(n)=1 satisfy the premises, but f(n) is not O(h(n)).
Statement "f(n)=o(g(n)) and g(n)=o(h(n)) β f(n)=o(h(n))": true. Proof sketch: f(n)/h(n) = (f(n)/g(n))Β·(g(n)/h(n)), and each factor tends to 0, so the product tends to 0.
Statement "f(n)=Ο(g(n)) and g(n)=Ο(h(n)) β f(n)=Ξ©(h(n))": true (in fact stronger). Since f(n)/g(n)ββ and g(n)/h(n)ββ, their product f(n)/h(n)ββ, so f(n)=Ο(h(n)), which implies f(n)=Ξ©(h(n)).
Final verdict: The small-o transitivity statement and the omega-based statement are both true. Therefore both of the statements that assert small-o transitivity and that omega-transitivity implies an Omega relation are correct.
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