## Search found 67 matches

- Fri Nov 06, 2009 5:13 pm UTC
- Forum: Mathematics
- Topic: "I'm thinking of a number..." game in a group
- Replies:
**13** - Views:
**2562**

### Re: "I'm thinking of a number..." game in a group

That doesn't mean it can't be solved. It just means we need to figure out what we mean by "optimal play". In particular, I think it should mean that players act to maximize their expected chance of winning, choosing randomly among the options available to them that do so (given that the ot...

- Tue Nov 03, 2009 11:56 pm UTC
- Forum: Mathematics
- Topic: "I'm thinking of a number..." game in a group
- Replies:
**13** - Views:
**2562**

### Re: "I'm thinking of a number..." game in a group

Why would the first player choose to play N/2 when they know that it will result in a 1/N chance of winning? Playing 2 would give them at least 2/N.

- Tue Nov 03, 2009 11:20 pm UTC
- Forum: Mathematics
- Topic: "I'm thinking of a number..." game in a group
- Replies:
**13** - Views:
**2562**

### Re: "I'm thinking of a number..." game in a group

For two players, the game is actually biased in favor of the first guesser. If the two players play optimally and are guessing between 1 and N, then when N is even, one will choose N/2 and the other will choose N/2 + 1 and both will have an equal chance of winning. If N is odd, though, then the firs...

- Tue Aug 25, 2009 11:36 pm UTC
- Forum: Mathematics
- Topic: Question on Gram-Schmidt Process.
- Replies:
**7** - Views:
**1203**

### Re: Question on Gram-Schmidt Process.

Do you not have a book? Or access to Wikipedia?

- Fri Aug 14, 2009 5:25 pm UTC
- Forum: Mathematics
- Topic: Signed Measure Clarification
- Replies:
**2** - Views:
**704**

### Re: Signed Measure Clarification

Well, if you use the wikipedia definition then I think it follows that in any signed measure space you just can't find a sequence of sets whose measures are conditionally convergent. So no problem! That seems...pretty wrong though. I think your requirement that having a conditionally convergent deco...

- Wed Jul 15, 2009 4:37 pm UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0610: "Sheeple"
- Replies:
**511** - Views:
**99649**

### Re: "Sheeple" Discussion

If you're not actively checking yourself against whim, instant gratification, etc, and just assuming that what you want = what's best for your life, you will obviously run in to these problems. This is all part of what is necessary to being rationally self-interested. Best for your life? What does ...

- Thu May 28, 2009 2:59 pm UTC
- Forum: Mathematics
- Topic: Recommended resources for teaching oneself Alg II?
- Replies:
**4** - Views:
**1151**

### Re: Recommended resources for teaching oneself Alg II?

I wouldn't worry about bothering your teachers. As long as you don't act like an arrogant smartass (which sounds unlikely based on your post), they'll probably be thrilled to find a student who's actually eager to learn. As for books, I'm not really sure. If you can get your hands on a copy of the b...

- Thu May 28, 2009 2:25 pm UTC
- Forum: Mathematics
- Topic: What's in a number?
- Replies:
**74** - Views:
**5927**

### Re: What's in a number?

The claim that definitions should be stated as "if and only if" has always struck me as confused. A definition is not a logical argument. It's...a definition. If you're not happy with, "A set with a binary operation is a group if blah blah blah" don't make it "if and only if...

- Thu May 28, 2009 2:17 pm UTC
- Forum: Mathematics
- Topic: Hypothesis testing
- Replies:
**8** - Views:
**1129**

### Re: Hypothesis testing

There's no need to bring normal approximations into this. You can just calculate the exact tail probability directly.

- Thu May 14, 2009 4:58 pm UTC
- Forum: Mathematics
- Topic: Submitting a paper
- Replies:
**14** - Views:
**1705**

### Re: Submitting a paper

Maybe "I'd ask the student to bring me back a list and help them decide how to rank them." is what you originally meant but to me, at least, it sounds quite different from "Good job. Now find a place to publish it."

- Wed May 13, 2009 9:36 pm UTC
- Forum: Mathematics
- Topic: Submitting a paper
- Replies:
**14** - Views:
**1705**

### Re: Submitting a paper

Indeed, and noting that a paper is of the quality to be published and encouraging the advisee to publish it is doing exactly that: "advising." However, the point of advising someone is to prepare them to become an independent academic. One thing one needs to learn for that purpose is how ...

- Wed May 13, 2009 9:19 pm UTC
- Forum: Mathematics
- Topic: Computer Random Number Generator - How?
- Replies:
**23** - Views:
**2186**

### Re: Computer Random Number Generator - How?

I think the problem with that scheme is more apparent if you work in base two (where you should probably be working anyway). When used to generate n digit (i.e. bit) numbers, it can only produce n different numbers. And those numbers are independent of your seed value. It probably becomes less bad a...

- Wed May 13, 2009 9:04 pm UTC
- Forum: Mathematics
- Topic: Ridiculously simple probability question
- Replies:
**18** - Views:
**1372**

### Re: Ridiculously simple probability question

Juuh, I got them to change their minds. They charged 1,50 instead of 1 euro. They had 40 pies and made about 80 euro profit. :P Err... So if you run the game by having 40 pies and having people play until the pies run out, then the total number of games played will be 40 + X where X has a negative ...

- Tue May 12, 2009 10:10 pm UTC
- Forum: Mathematics
- Topic: Ridiculously simple probability question
- Replies:
**18** - Views:
**1372**

### Re: Ridiculously simple probability question

What Ended said about the probabilities involved. Though the expected profit per game is going to be 0.42*(1 - 3) + (1-0.42)*1 = -0.26. Beyond that though, there's the question of how surprising a result turning a profit would be. To break even we have to have at least twice as many losses as wins a...

- Tue May 12, 2009 9:31 pm UTC
- Forum: Mathematics
- Topic: Submitting a paper
- Replies:
**14** - Views:
**1705**

### Re: Submitting a paper

quintopia wrote:If I were the advisor, I would have said "Good job. Now find a place to publish it."

The job of an advisor is to advise. I fail to see why this would apply to the publication process any less than anything else.

- Tue May 12, 2009 5:32 pm UTC
- Forum: Mathematics
- Topic: Submitting a paper
- Replies:
**14** - Views:
**1705**

### Re: Submitting a paper

If this was done during a REU program, don't you have a faculty advisor that you can (and probably should) discuss this with?

- Sat Apr 18, 2009 12:31 pm UTC
- Forum: Mathematics
- Topic: A Couple (easy?) Questions
- Replies:
**5** - Views:
**899**

### Re: A Couple (easy?) Questions

In general, it's the students job to actually *say* what logic they're using, so that the person grading can spend their time grading rather than on attempts at mind-reading. But of course, yes, you do have to do some mind reading sometime. But my mind-reading here didn't lead me to that conclusion....

- Sat Apr 18, 2009 10:45 am UTC
- Forum: Mathematics
- Topic: A Couple (easy?) Questions
- Replies:
**5** - Views:
**899**

### Re: A Couple (easy?) Questions

I wouldn't describe the reasoning for b as correct either. Just showing that you don't get the origin for two values of (a,b,c) doesn't show that you don't get it for any value of (a,b,c).

- Thu Apr 16, 2009 6:24 pm UTC
- Forum: Mathematics
- Topic: Number of subsets of bounded size.
- Replies:
**10** - Views:
**1283**

### Re: Number of subsets of bounded size.

I think that first approximation is not going to get you anywhere good. If we consider the quantity \sum_{k = 0}^{\sqrt{8n}} \frac{n^k}{k!} to be the \sqrt{8n} th Taylor approximation to e^n , then we get that this is equal to e^n - R_{\sqrt{8n}}(n) . Unless I screwed up somewhere, maximizin...

- Thu Apr 16, 2009 3:57 pm UTC
- Forum: Mathematics
- Topic: Singularics - Claims to prove RH by dividing by 0
- Replies:
**21** - Views:
**3540**

### Re: Singularics - Claims to prove RH by dividing by 0

Even if we were to accept that this was the work of a troll, the trollery would be so extensive as to be basically indistinguishable from mental illness. Mentally ill people exist and the chances of some random person on the internet being able to argue them out of their delusions is just about zero...

- Fri Apr 03, 2009 3:24 pm UTC
- Forum: Mathematics
- Topic: Function extrema in general
- Replies:
**9** - Views:
**1614**

### Re: Function extrema in general

I think what Yesila was going for is "f(x) is on the boundary of f(V)".

- Thu Apr 02, 2009 2:33 pm UTC
- Forum: Mathematics
- Topic: Measure theory problem - test preparation.
- Replies:
**10** - Views:
**1535**

### Re: Measure theory problem - test preparation.

Yeah, getting that 1/2 wasn't really necessary. It just seemed...right, though.

- Thu Apr 02, 2009 7:39 am UTC
- Forum: Mathematics
- Topic: Measure theory problem - test preparation.
- Replies:
**10** - Views:
**1535**

### Re: Measure theory problem - test preparation.

After thinking about this for a long time and writing up my solution, I reread and realized that I've come up with what I believe is the same solution as demon. As you say, Yakk, things took a strange left turn near the end of demon's last post, but I think this is (a slightly stronger version) of w...

- Fri Mar 27, 2009 10:21 pm UTC
- Forum: Mathematics
- Topic: Another Summation Question
- Replies:
**7** - Views:
**863**

### Re: Another Summation Question

And it wasn't even one of those ten-minutes-later "ninja'd"s. Still, I clearly am the winner.

- Fri Mar 27, 2009 10:10 pm UTC
- Forum: Mathematics
- Topic: Another Summation Question
- Replies:
**7** - Views:
**863**

### Re: Another Summation Question

Yeah, given that someone's teaching the class, I think you can assume that they tried the ratio test. I think you actually don't need any test at all (well, if you assume a certain well known series diverges):

**Spoiler:**

- Mon Mar 23, 2009 9:57 pm UTC
- Forum: Mathematics
- Topic: Definition of a gaussian stochastic process
- Replies:
**6** - Views:
**1002**

### Re: Definition of a gaussian stochastic process

but the multivariate normal condition is stronger than that - it says that every finite linear combination of the X t must be normally distributed. And yes, a multivariate normal distribution does not require that its components be independent. The given definition makes no mention of linear combin...

- Fri Mar 20, 2009 9:58 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0558: "1000 Times"
- Replies:
**266** - Views:
**49755**

### Re: "1000 Times" discussion

Please refrain from speaking about this subject until you have, at the very least, read the Wikipedia article on Keynesian economics. Virtually no one who actually studies how economies work thinks that what you're saying makes any sense. Just to be clear: not everyone agrees with Keynesian economi...

- Fri Mar 20, 2009 9:39 am UTC
- Forum: Individual XKCD Comic Threads
- Topic: 0558: "1000 Times"
- Replies:
**266** - Views:
**49755**

### Re: "1000 Times" discussion

I read somewhere that for every $1,000,000,000 spent by government, that's about $8 out of YOUR pocket. Well, if you read it somewhere, it must be true. If you take $1,000,000,000 and divide it by the number of taxpayers (138 million), then you get roughly $7.25 which I can only imagine is where th...

- Sat Mar 14, 2009 7:04 pm UTC
- Forum: Mathematics
- Topic: The Chow&Robbins problem
- Replies:
**19** - Views:
**2079**

### Re: The Chow&Robbins problem

Here's kind of a meta-question: can the optimal strategy be expressed (as, I think, the linked article implicitly assumes) by a function h(t) where you stop if your string has t tails and at least h(t) heads? My intuition says a very strong yes but it's not clear to me how to prove it. Absolutely. ...

- Sat Mar 14, 2009 6:47 pm UTC
- Forum: Mathematics
- Topic: The Chow&Robbins problem
- Replies:
**19** - Views:
**2079**

### Re: The Chow&Robbins problem

antonfire wrote:bray wrote:Eventually you're sure to get to 0.5 + epsilon.

No, you're not. You're sure to get above 0.5, but given epsilon>0, there is no guarantee that you will ever get to 0.5+epsilon.

Yes, I was being loose in my language. I just meant, "You'll get to something strictly greater than 0.5"

- Sat Mar 14, 2009 6:20 pm UTC
- Forum: Mathematics
- Topic: The Chow&Robbins problem
- Replies:
**19** - Views:
**2079**

### Re: The Chow&Robbins problem

So it seems any strategy that has an ending condition with 50% heads and 50% tails can certainly be improved. I guess you don't need such an ending condition to exist, but I'd at least call this strong evidence. 50/50 is a very special condition in this game, though. Namely, it's one that you can b...

- Fri Mar 13, 2009 9:32 pm UTC
- Forum: Mathematics
- Topic: What is wrong with this differentiation?
- Replies:
**19** - Views:
**2861**

### Re: What is wrong with this differentiation?

That definition is fine, I guess, but it's not clear to me what the point is. Yes, it reduces to normal summation when both limits of summation are integers, but so would an infinite number of other definitions. It does have the advantage over some other possible definitions that it turns the nonsen...

- Fri Mar 13, 2009 3:58 pm UTC
- Forum: Mathematics
- Topic: What is wrong with this differentiation?
- Replies:
**19** - Views:
**2861**

### Re: What is wrong with this differentiation?

Set x equal to any positive rational number, and define: \sum\limits_{i=1}^{a+b/c} f(x)+ =\sum\limits_{i=1}^{a} f(x)+f(x)\frac{b}{c} This only defines the sum when what you're summing is constant. And so it doesn't apply to any of the examples you gave. I'm assuming what you...

- Tue Mar 03, 2009 6:29 pm UTC
- Forum: Mathematics
- Topic: Augmented matrix
- Replies:
**12** - Views:
**1605**

### Re: Augmented matrix

So what, in particular, have you tried?

- Mon Feb 16, 2009 8:38 am UTC
- Forum: Mathematics
- Topic: The probability of impossible
- Replies:
**63** - Views:
**7536**

### Re: The probability of impossible

codyhotel wrote:Get it?

For future reference, the phrase "Get it?" is almost always going to just annoy whomever you're talking to. All the more so if what you've said immediately preceding it didn't actually make any sense.

- Fri Feb 13, 2009 3:37 pm UTC
- Forum: Mathematics
- Topic: The probability of impossible
- Replies:
**63** - Views:
**7536**

### Re: The probability of impossible

Even in describing it as an ideal dartboard, which I get, you still have a dart with an obviously non-zero area tip. Err...why? Assuming we're not throwing a non-ideal dart at our ideal dartboard, why wouldn't the dart have a tip that's a point? (And even if you chose not to for some reason, you co...

- Tue Feb 03, 2009 5:06 pm UTC
- Forum: Mathematics
- Topic: Number Theory Problem(s)
- Replies:
**8** - Views:
**1132**

### Re: Number Theory Problem(s)

I was about to claim that I had a third solution when I decided maybe I should check what Bertrand's postulate (which from now on I will call the Chebyshev-Bertrand theorem) was. I had forgotten that that thing had a name and assumed it was just a piece of folklore. The power of 2 solution is much m...

- Tue Feb 03, 2009 4:55 pm UTC
- Forum: Mathematics
- Topic: x - cos(x) = 0
- Replies:
**36** - Views:
**11291**

### Re: x - cos(x) = 0

Why? With enough digits it's trivial to compute the continued fraction representation of the Dottie number up to some desired accuracy and get good rational approximations. It's not a very useful exercise on a number that isn't known to have any nice algebraic properties. Because it's there. And, y...

- Tue Feb 03, 2009 4:49 pm UTC
- Forum: Mathematics
- Topic: Where'd I make my mistake? [Line integrals]
- Replies:
**5** - Views:
**1036**

### Re: Where'd I make my mistake? [Line integrals]

Man, seriously, what the hell. I should not do these things first thing after waking up. I have no idea what I was talking about since this is obviously not a complex analysis type line integral. My brain obviously just went, "Line integral. Zero. Cauchy's theorem." There's still a simple ...

- Tue Feb 03, 2009 3:02 pm UTC
- Forum: Mathematics
- Topic: Where'd I make my mistake? [Line integrals]
- Replies:
**5** - Views:
**1036**

### Re: Where'd I make my mistake? [Line integrals]

If you closed up your curve by including the segment along the y-axis then Cauchy's integral formula would tell you that the integral around that closed curve is zero. But your function is identically zero on that extra segment so the integral along the curve you're giving must also be zero.