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Jul
27
comment Recurrence relation with generating function problem
I agree; that's part of why it's less simple in this case.
Jul
22
comment Fast way to get a position of combination (without repetitions)
@van E.g. on SO: stackoverflow.com/questions/3143142/… stackoverflow.com/questions/5307222/… (and many others). On this site: math.stackexchange.com/questions/349924/… (and many others). On Wikipedia: en.wikipedia.org/wiki/Combinatorial_number_system en.wikipedia.org/wiki/Factorial_number_system Terms to search for are "(ranking|indexing) combinations", also "combinadics", and names of those WP articles.
Jul
22
comment Simple string permutations question
The answer is correct, but if you're writing it up for homework / an exam etc., you should add that $\binom{5}{2}$ is the number of ways to allocate the positions of the vowels in the sequence.
Jul
22
comment Playing roulette
@nknj: Thanks, fixed.
Jul
21
comment Fast way to get a position of combination (without repetitions)
This question has been asked before multiple times on both this website and StackOverflow; one of the existing answers may suit you. (That's assuming that your $\left(\!\!\binom{n}{k}\!\!\right)$ is just an odd way of writing $\binom{n}{k}$ because I don't know what else it could mean.)
Jul
15
comment What is the most efficient numerical base system?
@alex.jordan: Indeed, looks like I made exactly that mistake, thanks for pointing it out.
Jun
28
comment search on a split data structure
BTW, $b(n)$ is $n$ for the unsorted list as you always need to look at all elements before concluding it isn't there.
Jun
28
comment Special representation of a number
The remarkable resemblance of the two plots is interesting though, and I'm curious what the general shape (of the "upper" and "lower" curves) are.
Jun
28
comment search on a split data structure
It still wasn't clear so I've edited the question; take a look and see if that's what you intended.
Jun
28
comment search on a split data structure
Can you edit the question to make it clearer in the formatting which parts are quotation from the test / homework / question, and which parts are your own thoughts / questions?
Jun
26
comment How many algebras are there of finite-sized $\Omega$?
I just got a notification because this answer was upvoted. Not only do I have no recollection of having posted this answer, I don't even understand it now. At all. Clearly the explanation could have been better!
Jun
26
comment Expectation value of number of drawings of increasing sequences of labelled balls from an urn.
@uomoinverde The bounty doesn't matter so much; what would be gratifying would be if you indicated that you understood the ideas better now. :-)
Jun
26
comment Expectation value of number of drawings of increasing sequences of labelled balls from an urn.
Note that the question asks for the probability that the number of drawings is greater than $k$, but you seem to be calculating $\Pr(X \ge k)$ instead of $\Pr(X > k)$ (which is what it asks for).
Jun
18
comment How to determine growth rate of coefficients of generating function
@Michael Yes, their Chapter VIII on the saddle-point method covers such generating functions.
Apr
15
comment Maximizing profit (dynamic programming)
More precisely: how many of questions up to 18 did you solve? Why attempt 19?
Apr
15
comment Maximizing profit (dynamic programming)
Guess you need to first read about dynamic programming before solving exercises. Did you manage to solve all (or most) of questions 1 to 18, before attempting question 19?
Mar
22
comment Is this 5th root in the set of natural numbers?
What have you tried? What leads you to the belief that no such $x$ exists? If you include that in your question you are more likely to get an answer.
Mar
8
comment “What if” math joke: the derivative of $\ln(x)^e$
@bcrist: Ah I see... I was wrong, thanks for that!
Mar
7
comment “What if” math joke: the derivative of $\ln(x)^e$
@bcrist: Ah good point; perhaps one should say that though the What-If series contains references to the XKCD comics, there is none in the other direction. (Sort of how I can make references to a TV show, but a TV show will never make references to me.) At any rate, the subject of this question definitely doesn't count as "an xkcd", whatever that means. Nor is it even a joke, IMO.
Mar
7
comment “What if” math joke: the derivative of $\ln(x)^e$
@Ant: what-if.xkcd.com has nothing to do with the xkcd comic either, besides being hosted on the same domain. :-)