User talk:Phancy Physicist/Archive 1

Surveyor's Wheel

You added a maths description to surveyor's wheel without defining "a" or "b". A definition of these is necessary to make the description clear. A diagram would be nice. I've added a comment within the wikitext to note the necessary definitions. --Michael Daly (talk) 15:57, 28 September 2009 (UTC)[reply]

I think I fixed it thanks Phancy Physicist (talk) 20:25, 7 June 2010 (UTC)[reply]

Lennard-Jones potential

Hello. You removed the formula with A and B coefficients. Why?

-unsigned

First, thank you for checking up on a page edit. This is the section your are referring to.

==Alternative expressions==
The simplest formulation, often used internally by simulation software, is
: $V(r)={\frac {A}{r^{12}}}-{\frac {B}{r^{6}}},$ 
where A = 4εσ¹² and B = 4εσ⁶; conversely, σ = ⁶√A/B and ε = B²/(4A).

The equation with the A and B coefficients did nothing but replace one set of constants with another set of constants. Also, it is a dubious claim since,

V(r)=4\epsilon \left[\left\{\left({\frac {\sigma }{r}}\right)^{6}\right\}^{2}-\left({\frac {\sigma }{r}}\right)^{6}\right],

is more computationally efficient. This section didn't add anything to the article and its factually questionable.

Phancy Physicist (talk) 13:21, 28 December 2010 (UTC)[reply]

1. AB form is numerically more efficient and is used in almost all programs.

2. AB form traditionally used by computer chemists, in contrast to the sigma-epsilon form.

3. The coefficient B has the physical meaning (the magnitude of the dispersion interaction), in contrast to the sigma-epsilon form.

P99am (talk) 15:11, 28 December 2010 (UTC)[reply]

Responce to P99am:

1. If you pre-calculate A,B and 4ε then both methods take 5 operations. If you don't, the AB form takes 10 operations and the εσ form takes 6 operations. However, when pre-calculating the AB form has 2 divisions, 2 exponents and 1 subtraction whereas the εσ form has 1 division, 1 multiplications, 2 exponents and 1 subtraction. Multiplication is faster then division for a processor, allowing the εσ form to be called faster. If it truly is used by most programs, then supporting information needs to be given to make this claim.

2. If this form is traditionally used by computer chemists, then this information should be added to the section in that context to denote where its use comes from.

3. Again if this section is added back it should be done with more description as to why computational chemists use it and why A and B are useful to them. This added information would make the section a valuable contribution to the article.

If there is fault with my analysis in 1. please point it out to me.

Phancy Physicist (talk) 17:25, 28 December 2010 (UTC)[reply]

OK

1. Simplified code from a real program:

           r_2     = x*x + y*y + z*z;
           lIr     = 1.0 / sqrt (r_2);
           lIr_6   = lIr * lIr;    
           lIr_6 *= lIr_6 * lIr_6;
           VdW = (A * lIr_6 - B ) * lIr_6;

We never use two divisions. It's too long operation. (- 1, + 2, * 8, Sqrt 1, / 1)

Sigma-epsilon form is really prevalent in the theoretical literature. But in real programs and real calculations common form is AB. I believe that both forms should be presented in the article.

-unsigned

Responce to code

Sorry about the extra division. I have gotten the code that I use now for comparison.

Count the operations in your code: 6 variable writes, 1 division, 1 square root, 9 multiplication, 2 additions and 1 subtraction.

Code in εσ form:

           r_2     = x*x + y*y + z*z;
           lIr     = sig2/r_2;
           lIr_6   = lIr * lIr *lIr;    
           VdW = epsilon*lIr_6*(lIr_6 - 1);

Operation count: 4 variable writes, 1 division, 0 square root, 7 multiplication, 2 additions and 1 subtraction. You could possibly trade 2 multiplications for 1 exponent but the multiplication is faster.

Also what is the line,

           lIr_eps = lIr * lIepsilon;

for? I assume you mean:

           r_2     = x*x + y*y + z*z;
           lIr     = 1.0 / sqrt (r_2);
           lIr_6   = lIr * lIr;    
           lIr_6 *= lIr_6 * lIr_6;
           VdW = (A * lIr_6 - B ) * lIr_6;

Optimize your code a bit and get:

           r_2     = x*x + y*y + z*z;
           lIr     = 1 / r_2;
           lIr_6   = lIr * lIr * lIr;
           VdW = lIr_6*(A * lIr_6 - B );

Which would leave you with the exact same number and type of operations in my code.

You get almost identical speeds but the difference will end up being the time difference to divide 1 by a number and to divide a number by a number and the time it takes to subtract a number by 1 and a number by a number. I believe that the divisions take the same amount of time if so the εσ form would be slightly faster.

However this was not my point. My point was that without citations to back it up we can not claim that any algorithm is the most widely used. I agree that the AB form is worth putting in if you say why chemists prefer it and why A and B are useful. But not the way it is written now.

Phancy Physicist (talk) 19:36, 28 December 2010 (UTC)[reply]

I brought you a piece of real code. Real code takes into account not only what is written in Wikipedia, but also many other things. No doubts that this little piece can be rewritten no less effectively (but not more) into the sigma-epsilon form. But this changes nothing. AB form is more commonly used. There is no need to prove it. I simply confirm that the author of this paragraph was right. If you think that he was not, then you have to give the references. P99am (talk) 10:15, 29 December 2010 (UTC)[reply]

I also brought a real piece of code that I personally use and along with others in my research group. I simply changed the code variables to follow your example. I have shown that the two codes can be done almost identically. Again, you can not state that most of anything commonly uses something without proof. I not claiming that most use εσ form just that you need to proof it if you claim they mostly use AB. This discussion has gone longer than I thought it would and since It seems we will never agree, I am moving this to the talk page of the article.

Phancy Physicist (talk) 15:21, 29 December 2010 (UTC)[reply]

Your change in entanglement

Hi,

We've been having an interesting (and to me, productive) discussion.

I saw your change. I didn't want to revert it but I have some reservations about it.

However there is some debate about the underlying mechanism that enables this correlation to remain intact even when the separation distance is large.

To me, this formulation is too static. It sounds like a correlation gets set up in the BBO or wherever a twinned pair is created, and then that correlation just hangs tough no matter how far the members of the pair get separated. But the actual phenomenon, as I understand it, is dynamic. Quantum theoretically, at least, each photon (for instance) has a superposition of quantum characteristics, but ordinary macro experience would suggest that two photons should have two quantum states. Our naive expectations (even if we have the mind of Schrödinger) would be that photon spins should be unrelated. But that is not what we experience in the lab, and it turns out that Einstein made a good derivation from theory. The superpositions hang around at least until one photon gets "interrogated" by an experimenter or a passing speck of dust. Once one photon decoheres, it has a definite spin. Somehow, the other photon either decoheres at that time or is "preset" somehow to take on a complementary spin whenever it is interrogated and needs to show its spin. (I can't imagine any way to experimentally determine when the second photon decoheres. I think it's a moot point.) The correlation may "remain updated," but I don't think it remains "intact" in the way that the ice man "remained intact" in his glacier.P0M (talk) 08:34, 5 July 2011 (UTC)[reply]

I guess it does have the sound of enduring through all time which was not my intent. I changed it mostly to try and make it more in line with the usage of non-locality as User:Tercer pointed out. Maybe change "enables" to "allows" and "remain intact" to "exist"?

However there is some debate about the underlying mechanism that allows this correlation to exist even when the separation distance is large.

I think this helps it not sound so permanent. There is still something in the lead about decoherence so that aspect should be covered. Maybe decoherence should be mentioned first?

Phancy Physicist (talk) 17:30, 5 July 2011 (UTC)[reply]

I don't think the issue is with decoherence. At least that's not point at the problem I was seeing. How about:

However there is some debate about the underlying nature of reality that enables the maintenance of correlations between entangled twins even when the separation distances are large.

P0M (talk) 18:25, 5 July 2011 (UTC)[reply]

Combine them? I don't really want to use "twins" because entanglement can happen with more than two particles(states,state,whatever :) ). Maintenance makes it sound like something has to be done for the correlation to continue but the opposite is true something has to not happen, that is why I mentioned the decoherence thing. I do like getting rid of the "mechanism".

However there is some debate about the underlying properties of nature that allow this correlation to exist even when the separation distances are large.

Phancy Physicist (talk) 19:08, 5 July 2011 (UTC)[reply]

Concerning article "Elementary Algebra"

I saw your remarks of 10 June 2010 and agree. The section should be a cross-reference to the Wiki "Arithmetic" and contain very little else.

It is somewhat deficient in its explanation of the order of operations. If one takes too literally the injunction to perform multiplication before division and/or addition before subtraction, as implied by "PEMDAS", then problems can arise with expressions like 5 - 3 + 2 which will yield the wrong answer if addition is performed first in a naive way. Similarly 5 ./. 3 * 2 will be incorrect if the multiplication is first performed. The sub-chapter "Order of Operations" in the arithmetic article does better, indicating right to left order within multiplication/division and addition/subtraction. — Preceding unsigned comment added by 83.158.63.7 (talk) 13:27, 13 October 2011 (UTC)[reply]

JPY (disambiguation)

Hi. I've tagged JPY (disambiguation) for deletion under WP:CSD#G6, because it is only disambiguating two items of which one is the primary topic. I did a fairly lengthy search for other items to add to make this page valid but did not find anything. (If you know of others please add them now). When other items become available the page can be recreated, but generally there is no benefit in created "placeholder" or "in advance" dabs. I corrected the hatnote at Japanese yen so that those who are seeking John Paul Young can get to the article most easily. All the best, France3470 (talk) 17:44, 3 December 2011 (UTC)[reply]

That is fine was just on a currency code spree and I thought I would see if people would add more if the page existed. However I think that John Paul Young being linked on the Japanese yen page is a bit weird.

Phancy Physicist (talk) 19:17, 3 December 2011 (UTC)[reply]