Peter Shor
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 Apr22 comment Show $ex \leq e^x$ for all $x \in \mathbb{R}$ You've already made one mistake: $e - e^x$ is not always less than 0. Apr11 answered Example of pairwise independent random process with expected max load $\sqrt{n}$. Feb9 comment Integer Linear Programming You want $x_3$ to be as big as possible, and $x_1$ to be as small as possible. Use the greedy method to find $x_3, x_2,$ and $x_1$ satisfying the equations with these criteria (not necessarily integer). Now find the best integer solution. Think about the values of the variables mod 3. Oct27 comment Mathematician vs. Computer: A Game @pew: Isn't 30 the best choice for 31 as well? It ties with 5 and 7 for 32, but for 33 and above, the best choice seems to be prime. Oct14 awarded Yearling Sep30 awarded Good Answer Aug4 comment $q|2^p -1 \Longrightarrow p |q-1$ for primes $p,q$? Hint for first statement: use an elementary theorem from group theory. Aug4 comment Distributing half a deck of cards This seems like an ideal problem on which to use the inclusion-exclusion formula. Jul1 comment Number of unique permutations of a 3x3x3 cube Any arrangement can be rotated to yield 24 superficially different arrangements. You can put any of the six faces on the bottom, and then with that face on the bottom, o can rotate it to have any of four faces facing south. May18 answered Should I understand a theorem's proof before using the theorem? Apr8 awarded Nice Answer Mar30 comment A confusion about RP class of problems If the answer is incorrect, the machine will never accept. Thus, if the machine accepts, the answer is correct. It's the logical contrapositive. Oct14 awarded Yearling Oct4 comment Why are certain greek characters used predominantly for certain purposes in mathematics? @DonAntonio: my comment is meant to point out that this should really be treated as two separate questions: (a) why are Greek letters used in mathematics? and (b) why do certain letters get used predominantly for certain purposes? Sep28 comment Why are certain greek characters used predominantly for certain purposes in mathematics? This isn't specific to Greek letters. Why do $f$ and $g$ always stand for functions? Why is $i = \sqrt{-1}$? Why is entropy always represented by $H$ or $S$? Why is $\aleph_0$ the cardinality of countable sets? Sep7 comment Why variance in probability is taken as E[(X−E[X])2]? Why is this question being asked on cs.SE and not math.SE? Computer scientists did not define variance, and as far as I know, its usage in computer science is no different than its usage in math. Jul9 comment Rectangular Ground with Square tiles If $r\geq 2$, it is easy to prove that the minimum area has to be $81$ (since both edges must be at least $4r+1$). This is enough to show that the $r=1$ solution is minimal. Jul8 answered Rectangular Ground with Square tiles Jul4 comment Rectangular Ground with Square tiles Clearly, the ground is $0 \times 0$. There are no red tiles, and no white tiles, and since $0 = 0$, this satisfies the conditions. Jun24 revised What will be time complexity using dynamic programming found minor bug in my dynamic program