## Search found 3664 matches

- Sat Feb 07, 2009 3:53 pm UTC
- Forum: Mathematics
- Topic: Can I have your prime number?
- Replies:
**30** - Views:
**4807**

### Re: Can I have your prime number?

There's a nice prime counting formula, due to Riemann IIRC, that uses the (ordinary) zeta function. I coded this formula in C years ago. Here it is, in case anyone's curious. /* * R I E M * * A function found by Riemann for Pi(x), the number of primes <= x. * * These are the formulae, using a modif...

- Sat Feb 07, 2009 3:43 pm UTC
- Forum: Coding
- Topic: anything fundamentally wrong with...?
- Replies:
**26** - Views:
**2210**

### Re: anything fundamentally wrong with...?

Berengal wrote:Asserts are usually conditionally defined, so in release code it's nothing.

Exactly. So thinking of them as C's version of try...catch is somewhat misleading.

- Sat Feb 07, 2009 3:35 pm UTC
- Forum: Science
- Topic: Organic Vegetables
- Replies:
**73** - Views:
**4406**

### Re: Organic Vegetables

http://www.dhmo.org/ Welcome to the web site for the Dihydrogen Monoxide Research Division (DMRD), currently located in Newark, Delaware. The controversy surrounding dihydrogen monoxide has never been more widely debated, and the goal of this site is to provide an unbiased data clearinghouse and a ...

- Sat Feb 07, 2009 10:58 am UTC
- Forum: Mathematics
- Topic: golden ratio proof
- Replies:
**15** - Views:
**4368**

### Re: golden ratio proof

Are the colors in there due to colored lights, or has POV-Ray gotten sophisticated enough to model prisms? POV-Ray has been able to model dispersion for a while now, but it does slow down rendering a bit, as it has to trace more rays, so I rarely use this feature, and when I do I don't use many dis...

- Sat Feb 07, 2009 10:15 am UTC
- Forum: Coding
- Topic: anything fundamentally wrong with...?
- Replies:
**26** - Views:
**2210**

### Re: anything fundamentally wrong with...?

Asserts should not be active once the program has been released. They should only be active during the development phase.

- Wed Feb 04, 2009 12:01 pm UTC
- Forum: Coding
- Topic: anything fundamentally wrong with...?
- Replies:
**26** - Views:
**2210**

### Re: anything fundamentally wrong with...?

is there anything fundamentally wrong with using commas to string together what would otherwise be separate statements and ending the "block" with a semi I'll admit I was tempted to do this a few times, when I was young & foolish. :) And lived to regret it... I recommend avoiding this...

- Tue Feb 03, 2009 2:11 am UTC
- Forum: Mathematics
- Topic: golden ratio proof
- Replies:
**15** - Views:
**4368**

### Re: golden ratio proof

You may enjoy playing with the "Phibonacci" sequence Whoa... there's a part of me that wishes I did maths instead of physics... that is a very cool sequence. Now I'm trying to prove that the ratio of two adjacent Fibonacci numbers F(n)/F(n-1) approaches phi for n->infinity, but I am not s...

- Mon Feb 02, 2009 5:57 pm UTC
- Forum: Mathematics
- Topic: 1 + 1 = ?
- Replies:
**44** - Views:
**5648**

### Re: 1 + 1 = ?

I believe 1+1 was proven to be 2 around 1900 by Bertrand Russel. It was. I have a picture of his original work. Its a halarious paper long proof. He also spent a few hundred pages just laying the groundwork for it. Sort of. Russell & Whitehead were attempting to formalize mathematics, from the ...

- Mon Feb 02, 2009 5:42 pm UTC
- Forum: Mathematics
- Topic: Life and math
- Replies:
**21** - Views:
**2296**

### Re: Life and math

I reckon you ought to include as part of your presentation the Life form that generates the primes as a sequence of gliders. Another nice one is the recursive "unit cell": a Life form that simulates Life. It's probably more exciting than a simple Turing machine (although it pains me to say...

- Mon Feb 02, 2009 5:29 pm UTC
- Forum: Mathematics
- Topic: golden ratio proof
- Replies:
**15** - Views:
**4368**

### Re: golden ratio proof

You may enjoy playing with the "Phibonacci" sequence: \varphi^0 = 1 \varphi^1 = \varphi \varphi^2 = \varphi + 1 \varphi^3 = 2\varphi + 1 \varphi^4 = 3\varphi + 2 \varphi^5 = 5\varphi + 3 etc (Sorry about the poor formatting. I'd better learn some LaTex, I guess.:)) EDIT: This pic features ...

- Mon Feb 02, 2009 5:01 pm UTC
- Forum: Mathematics
- Topic: One of those questions on the philosophy of mathematics
- Replies:
**18** - Views:
**2556**

### Re: One of those questions on the philosophy of mathematics

The physical world can be modeled (to an extent) by mathematics. But conversely, the mathematical world can be modeled (to an extent) by physical objects. That doesn't mean that one is inherently more "real" than the other. To argue further, we need to define reality... It appears that man...

- Thu Jan 29, 2009 7:34 pm UTC
- Forum: Science
- Topic: Phase of one molecule
- Replies:
**14** - Views:
**1270**

### Re: State of one molecule

Temperature is usually defined as proportional to the mean kinetic energy of a whole bunch of molecules, so the temperature of a single molecule isn't well-defined, either. But I agree with the OP that the main issue is with the lack of intermolecular forces.

- Thu Jan 29, 2009 7:29 pm UTC
- Forum: Science
- Topic: Most silly "constant of nature"
- Replies:
**64** - Views:
**7161**

### Re: Most silly "constant of nature"

As long as we're being pedantic.... ... you can as easily have a mole of Carbon atoms as a mole of ping-pong balls... I doubt that. :) In theory, there is no difference between theory and practice. In practice, there is a huge difference between theory and practice. According to Wikipedia, the stan...

- Thu Jan 29, 2009 7:03 pm UTC
- Forum: Mathematics
- Topic: Favorite mental math tricks/shortcuts
- Replies:
**61** - Views:
**9546**

### Re: Favorite mental math tricks/shortcuts

(x^2 - y^2) = (x + y)(x - y) Very useful for the 10th graders I teach. I usually use this in the opposite direction. 17*13 = 15^2-2^2 = 221 Me, too. If you memorize the squares up to 25*25, and use a few other formulas, like (50 + x)^2 = (2500 + 100x +x^2) and (100 + x)^2 = (10000 + 200x + x^2) so ...

- Thu Jan 29, 2009 6:29 pm UTC
- Forum: Science
- Topic: After the big bang, where did pi, e and the rules originate?
- Replies:
**53** - Views:
**5362**

### Re: After the big bang, where did pi, e and the rules originate?

e, on the other had, is more "abstract" in the sense that we can't measure e like we measure pi. We can easily give a geometric definition for e. Draw the hyperbola xy = 1. The area under the branch in the ++ quadrant between x=1 & x=e is exactly one. And so is the area between x=e &a...

- Thu Jan 29, 2009 5:58 pm UTC
- Forum: Science
- Topic: Rapidly rotating wire
- Replies:
**52** - Views:
**3816**

### Re: Rapidly rotating wire

Alternatively, the problem can be analyzed in a rotating frame of reference centered on the wire's midpoint Can we? According to the OP: Lets say you have a long wire out in space, and you start spinning it very quickly around one end, so it looks sort of like a rope with a weight on the end being ...

- Thu Jan 29, 2009 5:39 pm UTC
- Forum: Mathematics
- Topic: objects that we'd like to hold, but can't in this universe
- Replies:
**41** - Views:
**6108**

### Re: objects that we'd like to hold, but can't in this universe

It's quite easy to make a flat model of a Klein bottle from paper & adhesive tape. Sure, it still self intersects, but you can cut it into a pair of Moebius strips with a pair of scissors. And regarding the projective plane, there are programs around that let you play with hyperbolic tessellatio...

- Thu Jan 29, 2009 5:06 pm UTC
- Forum: Mathematics
- Topic: Interesting sequences (Catalan, maybe?)
- Replies:
**42** - Views:
**3238**

### Re: Interesting sequences

I second t0rajir0u's nomination of derangements. The concepts are fairly easy to explain, and you can show the connection between the total number of permutations of n items (= n!) and number of derangements (= !n) and their relationship with e. I also like his idea of Beatty sequences, and not just...

- Thu Jan 29, 2009 4:38 pm UTC
- Forum: Mathematics
- Topic: Can I have your prime number?
- Replies:
**30** - Views:
**4807**

### Re: Can I have your prime number?

I think it's interesting to look at the primes from a complex POV. The Gaussian integers (complex numbers of the form a + bi, where a & b are both integers) have unique factorization. All the normal primes of the form 4n+3 are still prime in the Gaussians, all other primes have a Gaussian factor...

- Tue Jan 27, 2009 5:08 pm UTC
- Forum: Science
- Topic: Is consuming DNA safe? (not what you think. perverts.)
- Replies:
**39** - Views:
**5610**

### Re: Is consuming DNA safe?

You have to be really careful. Things labeled "75% ethanol" often contain methanol, which you definitely don't want to consume. That depends where you live. Some denatured ethanol does contain methanol, but it's pretty rare in Australia these days, and only used in certain applications. M...

- Tue Jan 27, 2009 4:37 pm UTC
- Forum: Mathematics
- Topic: x - cos(x) = 0
- Replies:
**36** - Views:
**10282**

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

Prof. Dottie Fixed and I think that's probably part of why the name is what it is. And my high school colleague never published his result, so his chance of glory was lost. Thus is the lot of the 'umble amateur. :) Speaking of iterating cos, Julia sets of complex trig functions can look quite prett...

- Tue Jan 27, 2009 4:25 pm UTC
- Forum: Mathematics
- Topic: Can I have your prime number?
- Replies:
**30** - Views:
**4807**

### Re: Can I have your prime number?

From Wikipedia: In number theory, Skewes' number is any of several extremely large numbers used by the South African mathematician Stanley Skewes as upper bounds for the smallest natural number x for which π(x) > li(x), where π(x) is the prime-counting function and li(x) is the logarithmic integral ...

- Tue Jan 27, 2009 4:08 pm UTC
- Forum: Mathematics
- Topic: Triangular Numbers
- Replies:
**9** - Views:
**1111**

### Re: Triangular Numbers

if we take the ratio of successive triangular squares, it converges to 17+12sqrt(2). How curious! Anyone familiar with the continued fraction of sqrt(2) will recognize 17/12 as a handy approximation of sqrt(2). Or for those who are more geometrically inclined, a 12, 12, 17 triangle is an isosceles ...

- Tue Jan 27, 2009 3:56 pm UTC
- Forum: Mathematics
- Topic: x - cos(x) = 0
- Replies:
**36** - Views:
**10282**

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

You can also just do n2 = cos(n1). No calculus needed. Certainly! But it takes ages to converge. If we use Newton's method, it converges rather rapidly. After the first couple of iterations, the number of correct digits doubles at each step. I tried this a few days ago using bc & was most impre...