Correlation Definition and 338 Threads

How can I find the correlation length of an auto-correlation? Is it the distance to the first zero of the auto-correlation? Is it the distance to the first min. of the auto-correlation? Is it the distance to the first max. of the auto-correlation? or should I integrate? Thank you

Do we need a coincidence counter (for correlation) in delayed erasure?...in case of repeating the same experiment many times (with one photon at a time) the same way In the DCQE experiment such as the one listed below http://grad.physics.sunysb.edu/~amarch/ Notice the polarizer...

hi, i want to learn about exponentially correlated random functions. can some one help me with some ideas or links or books. thanks in advance.

Hi all, I read on some paper that for a system of Fock state |...nk...>, and with the field operator expanded as \Psi(r)=\sumak \phik(r), the second order density correlation function can be expressed as G(2)=<\Psi+(r)\Psi+(r')\Psi(r')\Psi(r)>=<n(r)><n(r')>+|<\Psi(r)+\Psi(r')>|2-\sum^{N}_{k}...

Please teach me this: Why 2-point correlation function diagrams have only two external lines.Because of Wick theorem they would have many external legs. Another thing is whether are there odd number point correlation functions(meaning they are different from 0). Thank you very much in advanced.

Homework Statement The Fourier transform of the auto correlation function is the energy spectral density (ESD) of a signal. Here is the "apparent" proof: \int e^{-jwT} [ \int g(t)g(t+T)dt] dT => \int g(t)[ \int g(T+t)e^{-jwT}dT] dt What happened here? Why did the second integral change from...

Should one view correlation functions as: (1) \; \langle T{\phi(x)\phi(y)}\rangle or (2) \; \langle T{\phi(x)\phi(y)}\rangle - \langle \phi(x)\rangle \langle\phi(y)}\rangle with the second term being zero? (2) makes more sense as it really measures whether the two fields are...

I have a 2-dimensional field of values (they are actually heights of a surface) and I want to compute a correlation function or some sort of correlation parameter. I have seen something similar done with galaxies and you end up with something like the probability of finding a galaxy at a...

why is the redshift space correlation function smaller than the realspace correlation function at small scales and the opposite on large scales?

Science quiz question: How to determine the correlation between a car’s horsepower / torque and the maximum break strength of a cable that will hold the motor stationery. Assuming that the wheels of a car do not spin, how can I determine what the required cable’s break strength needs to be...

Hii, I was wondering whether there is any correlation between the energy eigenvalues of a single atom (say He) with the electronic band structure of a collection of He atoms. for example, for He atoms the lowest energy would be the ground state, with 2 electrons. So will the lowest band for a...

Hello all, I am currently building a model in Excel for predicting domestic water demand on a daily basis. The daily model will be compared to a more accurate model which runs on timesteps of 5 minutes (the latter is data intensive however which is why we are building a daily model as it...

Hi, everyone: I have been curious for a while about the similarity between the correlation function and an inner-product: Both take a pair of objects and spit out a number between -1 and 1, so it seems we could define a notion of orthogonality in a space of random variables, so...

Hi, I have a problem in calculating the second order correlation (coherence) from the master equation for the operators \sigma and a a[+][/SUP] , because I don't know if <aa^{+}a^{+}a> can be factorized to<a><n><a>. I want to do this calculation directly from the density matrix solution. thanks

I'm trying to prove that abs(r) <= 1. (Ill apologize up front that I am not sure on how to write all equations properly in this forum, but Ill try to make it clear) Note that this is all sample statistics, not population, which is why I'm using r and not rho. I know that I have to use...

I wonder, what the physical meaning to electron correlation in molecular systems? and. Is there many types of it? Thanks for interest colleagues

Hi, I am going through Non Equilibrium Statistical Mechanics by Zwanzig and I can't follow, the step below: I have the equation: <x^{2}> = \int^{t}_{0}ds_{1}\int^{t}_{0}ds_{2}<v(s_{1})v(s_{2})> I can't show that: \frac{\partial <x^{2}>}{\partial t} = 2 \int^{t}_{0}ds<v(s)v(t)>...

The thing I don't understand is how does finding out the median help you drawing in the horizontal and vertical lines. How do you know if it's going to pass through a few of the data points? Like in the example on that website it has a moderate negative correlation and the median is the 8'th...

I am writing a paper publishing scientific data. My background is chemistry but I have taken a couple of stat classes. In my opinion, one of the biggest deficiencies in modern research publications is the improper use of statistics. I hope to avoid making this mistake, but I need your help...

So there was a thread: https://www.physicsforums.com/showthread.php?p=2847138#post2847138 about IQ and being successful that I think is an interesting topic and is worthy of discussion so I thought I'd start a new thread here. The reason for doing so is that I was recently reading Malcolm...

I have the following problem: Suppose there is a survey of persons with two properties each (a and b). a can take a relatively small number of values (say the political inclination: Conservative, Liberal, Socialist, or Other) the other one b can take a large number of values (say: the country...

Hi, Does anyone know if there's a closed formula for the n-point function in a CFT? Up to anharmonic ratios, of course. Most books just have it up until n=4. Thanks, Matt

Hi guys, I have data of 20 peoples height, weight, calorie intake and skinfold thickness. I have carried out a regression of calorie on height, on weight and on height and weight. I have done the same thing for skinfold thickness. I then used R to work out the summary of results. each...

I've been looking at some of the more prestigious graduate programs in physics and I've noticed in photographs that all of the grad students look very young. On the Princeton website, I couldn't spot one that looked over 25. Is it fair to say that more prestigious institutions tend to avoid...

Say I have 2 separate predictor variables x and y. And the response variable is z. The correlation between x and z is a; the correlation between y and z is b. How to get the p-value for a = b? By using SAS or SPSS. I believe we should use t-test. Because the correlation analysis for...

Hi there, I am learning the basics of QFT at the moment. Could someone explain to me, in the case for any number of scalar fields, the difference between correlation functions and scattering amplitudes please? Correlation functions <0|T(\phi_{1}...\phi{n})|0> Does one always write the...

Does anyone know why: <m(k)m(p)>=(2 \pi)^3 \delta(k+p)|m(k)|^2 where m(k) and m(p) are the Fourier transform of the order parameter density and the angled brackets <> stand for an ensemble average? For example, the magnetization M is given by: M=<\int d^3r m(r)>

Why are they useful, what do they denote (physically or otherwise)...

Homework Statement For my homework i have to compute a correlation function in excel from available data. Data goes somewhat like this: 1 xxx yyy 2 xxx yyy 3 xxx yyy I now I have to calculate...

I am searching for correlation with science and atheism/agnosticism. If this thread conflict with the rules (which I don't think it does), I accept that. If so, just remove it. If allowed: Discuss the correlation between science and atheism/agnosticism.

First off, thanks for taking the time to read this. I am not a Physics Major, I am not a scientist. I do try to think a great deal about our existence, and what our future holds as far as discovery, so therefore, I have something to present. It is hypothetical, but please play along with it...

1. Let N and T be the number of users logged on and the time until the next log-off. The joint probability of N and T is given by P(N=η, X≤t) = (1-ρ)ρ^{η-1}(1-e^{-ηλt}) for η=1,2,...;t>0.) Find the correlation and covariance of N and T. 2. COV(X,Y) = E[XY]-E[X]E[Y] ρ_{X,Y} =...

Hi, I can't get my head around this question. Homework Statement The Bell state: |\psi\rangle = \frac{1}{\sqrt{2}}\left(|\uparrow_1\rangle|\downarrow_2\rangle +|\downarrow_1\rangle |\uparrow_2\rangle \right) Find the correlation coefficient of the measurement of the spins in the directions...

matter in The universe is thought to be made up of 75 percent hydrogen and helium is thought to make up 25 percent of helium; Dark matter is thought to make up 25 percent of the universe and 75 percent dark energy; that's an interesting coincidence. , and currently physicists are not certain...

Dear all I have the following problem. Given a set of correlated binary variables, can I determine the joint probability from the correlation function? {Xi} is a set of binary variables Pr(Xi=1) = p and Pr(Xi=0) = q for all i Corr(Xi Xj) = cij cij is symmetric Now how can I determine the...

Correlation between "Snowball Earth" and Cambrian Explosion I know there is a theory that the Earth was once covered in ice that precisely pre-dates the cambrian explosion. is there a leading idea of how snowball Earth allowed for the blossoming of multicellular organisms? Did the ice sheets...

I'm trying to understand the Wiener Filter, and I have a few questions. 1. How can there be such a thing as a correlation matrix of 1 vector. I read here: R_yy = E[ y(k) * y^T(k) ] where y(k) is a vector, and y_T(x) is the same vector transposed. I thought correlation represents the...

(I moved this from the Homework section. I hope it is okay I am posting here.) Homework Statement We are given six cross sections each spaced 2km apart and from these we are supposed measure the slip of the fault, and map the hanging-wall and footwall cutoffs to another worksheet that is...

is there any corrolation between thermal conductivity coefficient and molecular wieght Mw according to the units [K] W/(m·K) it is independant of mass units (kg or g/mol etc) in my question i am asked to show with a graph, but i have no idea what graph they are talking about

Hi all, The correlation coefficients (Pearson's) is usually defined in terms of discrete sampling of a function. However, I have seen that the mean and standard deviation, for example, are also typically written in terms of discrete variables BUT may also be expressed in terms of a...

Hi everyone, I'm working through Section 9.2 (Functional Quantization of Scalar Fields) from Peskin and Schroeder. I have trouble understanding the absence of a term in equation 9.41 which I get but the authors do not. Define \phi_i \equiv \phi(x_i), J_{x} \equiv J(x), D_{xi} \equiv...

Can someone tell me where algal blooms occur? I'm basically interested in knowing if they're more frequent in certain latitudes (colder regions).

[SIZE="7"][SIZE="5"]I offer you the solution of a fundamental problem of physics: the relationship between the matter (body) and the field. Many outstanding minds in theoretical physics, including Einstein, tried to resolve this problem, but failed. If 1924 French physicist Louis de Broglie...

Hi everyone I am trying to get equation 4.29 of Peskin and Schroeder from equation 4.28. This is what I did |\Omega\rangle = \lim_{T\rightarrow\infty(1-i\epsilon)}\left(e^{-iE_{0}(t_{0}-(-T))}\langle\Omega|0\rangle\right)U(t_0, -T)|0\rangle Take the Hermitian Adjoint of both sides. \langle...

Hi, I was going through section 9.2 of Peskin and Schroeder, and came across equation 9.16 which reads \int\mathcal{D}\phi(x) = \int \mathcal{D}\phi_{1}({{\bf{x}}}) = \int \mathcal{D}\phi_{2}({{\bf{x}}}\)int_{\phi(x_{1}^{0},{\bf{x}})\\\phi(x_{1}^{0},{\bf{x}})}\mathcal{D}\phi(x) What does the...

correlation, linear or curvilinear... Hello Forum, usually the Pearson coefficient is meaninful to find the linear relationship between two variables. What if the relationship is not linear? How about quadratic? I heard of the Spearman’s rank correlation coefficient, which does not depend...

Hello people, I don't understand the relation between those concepts, I tried to read what's written in wikipedia about them but no use. Can someone please elaborate more about the relation between them in some intuitive manner? Thank you :)

1 Let X be a normal variable with mean 0 and variance 1. Let Y = ZX where Z and X are independent and Pr(Z = +1) = Pr(Z = -1) =1/2. a Show that Y and Z are independent. b Show that Y is also normal with mean 0 and variance 1. c Show that X and Y are uncorrelated but dependent. d Can you...

Does anyone know if there is any correlation between these two?I mean most of the times during El Nino events the weather here in Europe gets ''crazy'' but till now i haven't seen any formal scientific survey which describes it with certainty. Now with the new El Nino being formed what kind of...

I can generate two random sequences X[i] and Y[i] with no correlation. For example, X[i] = rand(0,1) Y[i] = 100 + rand(0,1) Now, if I plot Y as a function of X, and scale it to a square, I get a random distribution of points showing no correlation (as expected)...