update notations and fix typos
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@@ -96,7 +96,7 @@ We wait for $R$ times and then take the stairs. In worst case, we wait for $R$ t
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Competitive ratio = $\frac{2R}{R}=2$.
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EOP
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QED
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Let's try $R=S-E$ instead.
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@@ -116,7 +116,7 @@ We wait for $R=S-E$ times and then take the stairs.
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Competitive ratio = $\frac{S-E+S}{S}=2-\frac{E}{S}$.
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EOP
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QED
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What if we wait less time? Let's try $R=S-E-\epsilon$ for some $\epsilon>0$
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@@ -174,7 +174,7 @@ The optimal offline solution: In each subsequence, must have at least $1$ miss.
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So the competitive ratio is at most $k+1$.
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EOP
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QED
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Using similar analysis, we can show that LRU is $k$ competitive.
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@@ -184,7 +184,7 @@ Split the sequence into subsequences such that each subsequence LRU has $k$ miss
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Argue that OPT has at least $1$ miss in each subsequence.
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EOP
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QED
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#### Many sensible algorithms are $k$-competitive
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@@ -210,7 +210,7 @@ So competitive ratio is at most $\frac{ck}{(c-1)k}=\frac{c}{c-1}$.
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_Actual competitive ratio is $\sim \frac{c}{c-1+\frac{1}{k}}$._
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EOP
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QED
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### Conclusion
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@@ -297,7 +297,7 @@ Let $P$ be a page in the cache with probability $1-\frac{1}{k}$.
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With probability $\frac{1}{k}$, $P$ is not in the cache and RAND evicts $P'$ in the cache and brings $P$ to the cache.
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EOP
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QED
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MRU is $k$-competitive.
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@@ -317,4 +317,4 @@ Let's define the random variable $X$ as the number of misses of RAND MRU.
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$E[X]\leq 1+\frac{1}{k}$.
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EOP
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QED
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@@ -161,7 +161,7 @@ $ISET(G,k)$ returns true if $G$ contains an independent set of size $\geq k$, a
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Algorithm? NO! We think that this is a hard problem.
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A lot of people have tried and could not find a poly-time solution
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A lot of pQEDle have tried and could not find a poly-time solution
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### Example: Vertex Cover (VC)
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@@ -154,7 +154,7 @@ This is a valid assignment since:
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- We pick either $v_i$ or $\overline{v_i}$
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- For each clause, at least one literal is true
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EOP
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QED
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Claim 2: If $\Psi$ is satisfiable, then Subset Sum has a solution.
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@@ -174,7 +174,7 @@ Say $t=\sum$ elements we picked from $S$.
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- If $q_j=2$, then $z_j\in S'$
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- If $q_j=3$, then $y_j\in S'$
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EOP
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QED
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### Example 2: 3 Color
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@@ -228,13 +228,13 @@ For each dangler color is connected to blue, all literals cannot be blue.
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...
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EOP
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QED
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Direction 2: If $G$ is 3-colorable, then $\Psi$ is satisfiable.
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Proof:
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EOP
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QED
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### Example 3:Hamiltonian cycle problem (HAMCYCLE)
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@@ -153,7 +153,7 @@ Summing over all vertices, the total number of crossing edges is at least $\frac
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So the total number of non-crossing edges is at most $\frac{|E|}{2}$.
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EOP
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QED
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#### Set cover
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@@ -264,7 +264,7 @@ So $n(1-\frac{1}{k})^{|C|-1}=1$, $|C|\leq 1+k\ln n$.
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So the size of the set cover found is at most $(1+\ln n)k$.
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EOP
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QED
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So the greedy set cover is not too bad...
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@@ -350,4 +350,4 @@ $$
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So the approximation ratio for greedy set cover is $H_d$.
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EOP
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QED
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@@ -296,7 +296,7 @@ If $c'\geq 8c$, then $T(n)\leq c'n\log n+1$.
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$E[T(n)]\leq c'n\log n+1=O(n\log n)$
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EOP
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QED
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A more elegant proof:
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@@ -345,5 +345,5 @@ E[X]&=\sum_{i=0}^{n-2}\sum_{j=i+1}^{n-1}\frac{2}{j-i+1}\\
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$$
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EOP
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QED
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