## Search found 34 matches

Wed May 27, 2009 2:05 am UTC
Forum: Mathematics
Topic: A question about random walks
Replies: 33
Views: 2981

### Re: A question about random walks

Am I talking to zombies here? 24 hours of defense preparation is making me very irritable... nevermind, sorry about that rhino... i need to grab some sleep but I'll just make the point clear. for any p > .5, P(x_i = 0, i \in \mathbb{N}) = \sum_{n=1}^{\infty} (1-p)^n = \frac{1-p}{p} ^...
Wed May 27, 2009 1:38 am UTC
Forum: Mathematics
Topic: A question about random walks
Replies: 33
Views: 2981

### Re: A question about random walks

In any case, the focus is the conditional probability P(x_{2n-1} = 0 | x_i > 0, \forall i < 2n -1) . For this to occur, there has to be exactly n number of downward paths each with the probability (1-p). anything more would imply that x_{2n-1} < 0 , anything less would imply that x_{2n-1} > ...
Wed May 27, 2009 1:26 am UTC
Forum: Mathematics
Topic: What's in a number?
Replies: 74
Views: 5760

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

t0rajir0u wrote:
Haeche wrote:a number is an axiomatic definition that we find useful.

But this definition is too vague to be correct. We make plenty of axiomatic definitions that nobody would call numbers.

it's a specific axiomatic definition that we find useful.
Wed May 27, 2009 1:19 am UTC
Forum: Mathematics
Topic: A question about random walks
Replies: 33
Views: 2981

### Re: A question about random walks

Here I coded it in matlab for you clear count = 0; p=.6 N=10000; for n = 1 : N i = 1; x(1) = 1; while (x(i) ~= 0 && i <= 10000) if rand < p x(i+1) = x(i) + 1; else x(i+1) = x(i) - 1; end i = i+1; end if x(i) == 0 count = count + 1; end end [count/N, 1/(p)-1] pick any p > .5 and you'll get an...
Wed May 27, 2009 1:07 am UTC
Forum: Mathematics
Topic: A question about random walks
Replies: 33
Views: 2981

### Re: A question about random walks

the probability that x_{2n-1} would hit 0 conditional that it hasn't hit it before is (1-p)^n. There is no way that this is correct. The answer should be in terms of Catalan numbers if you're setting x_0 = 1 (which is a strange convention some people in this thread appear to be following; x...
Tue May 26, 2009 4:05 pm UTC
Forum: News & Articles
Topic: California eliminating welfare
Replies: 90
Views: 7296

### Re: California eliminating welfare

My hero, Paul Krugman, wrote a nice column today about the situation facing california. http://www.nytimes.com/2009/05/25/opinion/25krugman.html Ah, yes, blame it all on the Republicans. Notice Krugman's claim that this would have been avoided, if California was using more property taxes and less i...
Tue May 26, 2009 2:59 pm UTC
Forum: News & Articles
Topic: Obama Nominates Sotomayor for Supreme Court
Replies: 208
Views: 14743

### Re: Justice David Souter to retire at the end of June

Diversity is a huge +. Love to have a hispanic lady on the court. Granted that she's non-controversial, pragmatic, and god forbid capable, but maybe the drama queen in me wanted a liberal counterpart to the alitos and the thomases.
Tue May 26, 2009 1:27 pm UTC
Forum: Mathematics
Topic: A question about random walks
Replies: 33
Views: 2981

### Re: A question about random walks

I'm reasonably certain, although i don't have a proof on hand, that formula for the geometric series of (1-p), \frac{1-p}{p} , is the probability, for p > .5, that the process in question hits 0 sometime in an infinite iteration. For any p <= .5, the state variable will hit 0 given enough time. <edi...
Tue May 26, 2009 12:45 pm UTC
Forum: Mathematics
Topic: A stochastic process question
Replies: 2
Views: 737

### Re: A stochastic process question

you did your algebra wrong. It's E[W_s(W_s+(W_t-W_s))] = E[W^2_s+W_s(W_t-W_s)] = E[W^2_s] + E[W_s (W_t-W_s)] remember that by definition, (W_t-W_s) is independent from W_s , so you can factor and obtain =E[W^2_s] + E[W_s] E[W_t-W_s]. Since E[W_t-W_s] = 0, we o...
Tue May 26, 2009 8:49 am UTC
Forum: Mathematics
Topic: What's in a number?
Replies: 74
Views: 5760

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

a number is an axiomatic definition that we find useful. You can't really break it down any further than that. If you try to define it in terms of quantity or amount you'll be playing a self referencing game that can't be won. What's a number? An amount. What's an amount? a number. I'm rather remind...
Mon May 25, 2009 3:36 pm UTC
Forum: News & Articles
Topic: Senator Bob Graham, Nerd, may just pwn the CIA
Replies: 33
Views: 3554

### Re: Senator Bob Graham, Nerd, may just pwn the CIA

Given Graham's testimony, CIA has more questions to answer than Pelosi. Regardless of media bias, why are we more inflamed at Pelosi than at the fact that THE CIA IS TORTURING PEOPLE?
Mon May 25, 2009 3:33 pm UTC
Forum: News & Articles
Topic: I may be Legend (possible cancer cure)
Replies: 27
Views: 3176

### Re: I may be Legend (possible cancer cure)

I'm rather doubtful about the whole thing. If the work could possibly cure cancer as it claims then why is it published in PLoS Pathogens instead of journals of more repute like Science or Cell, not to mention Lancet or NJM.
Mon May 25, 2009 3:19 pm UTC
Forum: News & Articles
Topic: Conservative waterboarded for charity, not hannity
Replies: 10
Views: 2073

### Re: Conservative waterboarded for charity, not hannity

I dislike hannity as well
Mon May 25, 2009 3:13 pm UTC
Forum: News & Articles
Topic: California eliminating welfare
Replies: 90
Views: 7296

### Re: California eliminating welfare

My hero, Paul Krugman, wrote a nice column today about the situation facing california.

http://www.nytimes.com/2009/05/25/opini ... ugman.html
Mon May 25, 2009 3:03 pm UTC
Forum: News & Articles
Topic: Senate shoots down Obama's plan to close Guantanamo
Replies: 54
Views: 4468

### Re: Senate shoots down Obama's plan to close Guantanamo

We made it a huge deal whenever China or the old Soviets wrongfully imprisoned an accused for years without charge, but now we're doing the same. Obama, where the f__k is the change you promised? The only way to regain america's moral compass is to take some risks. If this means releasing dangerous ...
Mon May 25, 2009 2:56 pm UTC
Forum: News & Articles
Topic: North Korea carries out 2nd nuclear test
Replies: 111
Views: 9085

### Re: North Korea carries out 2nd nuclear test

I'm moving back to Cleveland. No one would waste a nuclear missile on that dump.
Mon May 25, 2009 2:42 pm UTC
Forum: Mathematics
Topic: Why is calculus considered so complex?
Replies: 64
Views: 6795

### Re: Why is calculus considered so complex?

In my experience, there's always something "harder" than what you've done before. After algebra, there's formal calculus, then functional analysis, after that there's measure theory, probability, etc... Calculus is as a good point as any other to be considered complex.
Fri May 22, 2009 3:12 am UTC
Forum: News & Articles
Topic: Texas Universities and concealed handguns.
Replies: 54
Views: 4689

### Re: Texas Universities and concealed handguns.

Why? Concealed handguns decrease crime. You know the econometric models that suggest that assume something like crime=a*ConcealedHandGunLaw+b*blah+... i.e. the model is linear at the region of the existing exogenous data. So even though concealed handguns laws may decrease crime in the state we are...
Fri May 22, 2009 1:12 am UTC
Forum: News & Articles
Topic: Wolfram Alpha Tricks and Randomness
Replies: 69
Views: 10864

### Re: Wolfram Alpha Tricks and Randomness

Klapaucius wrote:It knows all this about Cinnamon Toast Crunch, but still can't figure out the one fact that matters.

Also, I found one question that it will ALWAYS get right.

what's the one fact that matters? (the links are the same). there's swirls in every bite?
Tue May 19, 2009 12:22 am UTC
Forum: News & Articles
Topic: Wolfram Alpha Tricks and Randomness
Replies: 69
Views: 10864

### Re: Wolfram Alpha Tricks and Randomness

they really should just open up part of the server to as many contributors as possible while protecting some of the more manipulatable datasets. (sets where people might not notice if you move the data slightly one way or another). From what I can tell, alpha is really meant to compete against wikip...
Mon May 18, 2009 3:54 am UTC
Forum: News & Articles
Topic: Wolfram Alpha Tricks and Randomness
Replies: 69
Views: 10864

### Re: Wolfram Alpha Tricks and Randomness

Sweet Scooby! about 2500 drinks = 100% blood alcohol!!! I might die afterward, but my blood is gonna taste like champagne tonight!
Sun May 17, 2009 10:54 am UTC
Forum: Computer Science
Topic: Wolfram|Alpha
Replies: 77
Views: 10251

### Re: Wolfram|Alpha

Without seeing this thread, I kind of posted a new one about Alpha in the news section. We've sort of changed it into finding as many unusual answers on Alpha as possible topic instead. Check it out here: viewtopic.php?f=9&t=39339
Sun May 17, 2009 4:41 am UTC
Forum: News & Articles
Topic: Explorer scouts
Replies: 31
Views: 3822

### Re: Explorer scouts

It worries me too. On one hand kids will be kids and this might be a more "grown-up" version of the cowboys and indians game that we all partook when we were younger. I hate the fact that it turns what might be fun about playing cops and robbers into a "scout" organization with a...
Sun May 17, 2009 3:24 am UTC
Forum: News & Articles
Topic: Wolfram Alpha Tricks and Randomness
Replies: 69
Views: 10864

### Re: Wolfram Alpha

Sat May 16, 2009 5:30 pm UTC
Forum: News & Articles
Topic: Wolfram Alpha Tricks and Randomness
Replies: 69
Views: 10864

### Re: Wolfram Alpha

I completely agree. The database is quite underdeveloped and the demo seems to be rather rigged. Anyway the package seems to have a good amount of mathematica's symbolic computational capacity even though it uses intuitive/more lingustic inputs. Try typing in fourier transform Sin[t^2] or whatever e...
Sat May 16, 2009 3:46 pm UTC
Forum: News & Articles
Topic: Wolfram Alpha Tricks and Randomness
Replies: 69
Views: 10864

### Wolfram Alpha Tricks and Randomness

I've been playing with this all day. The science package is still a little underdeveloped and not as intuitive as the demo claims it to be; but aint it cool to be able to get the Fourier transform of a symbolic function with nothing but a standard web browser? http://www.wolframalpha.com/screencast/...
Sat May 16, 2009 2:05 pm UTC
Forum: Mathematics
Topic: ITT: Why Math Is Awesome.
Replies: 51
Views: 6340

### Re: ITT: Why Math Is Awesome.

Some physicists and philosophers believe that the physical universe is isomorphic to a mathematical structure, but I'm not complete sure that that is the entire reason for its awesomeness. To a student/amateur like me, math is the most advanced endeavor to understand the logical structures our minds...
Wed May 06, 2009 8:33 am UTC
Forum: Mathematics
Topic: Math Books
Replies: 379
Views: 280300

### Re: Math Books

Don't mean to post twice, but just wanted to tell everyone that Dover's series on various mathematics is pretty awesome. I'm using Gelfand and Fomin's Calculus of Variations right now to brush up on the topics, and I'm definitely impressed. A couple other graduate students I know had nothing but goo...
Sun May 03, 2009 6:25 am UTC
Topic: 0135: "Substitute"
Replies: 84
Views: 67508

### Re: "Substitute" discussion

I posted my solution here.

The latex solution can be directly linked here.
Sun May 03, 2009 4:33 am UTC
Forum: Mathematics
Topic: Help with a Math Problem
Replies: 11
Views: 1724

### Re: Help with a Math Problem

What's jamming up the circuits? Hint, start by writing down the problem and the terms one by one.
Sun May 03, 2009 4:30 am UTC
Forum: Mathematics
Topic: Math Books
Replies: 379
Views: 280300

### Re: Math Books

If you're interested in more advanced mathematics, I have a list some where. I'll try to dig it up one day. Out of the top of my head, I was very impressed by Trefethen's Numerical Linear Algebra. If anyone is interested in Stochastic Calculus, I have a review of a couple books here.
Sun May 03, 2009 4:28 am UTC
Forum: Mathematics
Replies: 43
Views: 5680

I would marry my old Ti-89 if I could find it.
Sat May 02, 2009 9:25 pm UTC
Forum: Mathematics
Topic: LaTeX and other markup!
Replies: 73
Views: 35691

### Re: LaTeX and other markup!

very nice. well... that was my first post. hallo folks
Sat May 02, 2009 9:23 pm UTC
Forum: Mathematics
Topic: LaTeX and other markup!
Replies: 73
Views: 35691

### Re: LaTeX and other markup!

[imath]\pi(x|y) = N\left(\mu_x + \frac{\sigma_{xy}}{\sigma_y^2}(y-\mu_y),\sigma_x^2(1-\rho_{xy}^2)\right)[/imath]