# Search results

1. ### Finding the sine of the angle between 2 rays

Hello, say you are on the unit sphere and you have 2 rays intersecting it from the origin. You know the spherical coordinates of where these 2 rays intersect the sphere ##(\theta_1,\phi_1),(\theta_2,\phi_2)##. Now, because we know the dot product of two vectors, it is simple to get that the...
2. ### Fortran [Fortran] Quick question about complex exponentials

Hey, so I just have a quick question. I am trying to set a complex variable (in an array) as ##e^{i\alpha_1}## and the line I used in my code looks like this: hmajphasemix(2,2)=(cos(alpha1),sin(alpha1)) But the compiler is telling me that it "expects a right parenthesis" at this line. I'm...
3. ### Fortran [FORTRAN] How did I screw up my code?

Hi guys, there's a bug in my code which I've been trying to get rid of for the last 2 weeks. I'm completely out of ideas now on what it is so I have to turn to you guys for help. The code is here: module helectron use params use parallel !* electron density parameters integer ...
4. ### Fortran [FORTRAN] Code misassigning values

Hi guys, I can't figure this one out. Here I am working with a piece of code which should read in a grid of 2 arrays, a radius array and an electron fraction array. The code looks like this: subroutine varelec_init(varelecfrac,elecprofile,effilename,elecfracname) integer ...
5. ### Are Jacobi fields defined at intersection points?

I have some questions with regards to conjugate points on a congruence of time-like geodesics (will be referring to Wald 9.3 throughout). First, we define ##\gamma## to be a time-like geodesic with tangent ##\xi^a## parametrized by ##\tau## and with ##p\in\gamma##. We consider the "congruence of...
6. ### Remind me why FLRW curvature can't switch between cases

Hi, as we all know, the FLRW metric has 3 types of spatial curvatures, spherical, flat, and hyperbolic. I understand that of course due to homogeneity, this curvature must be spatially everywhere the same and so can not depend on the spatial coordinates. However, I can't recall what is the...
7. ### Proper mass vs Schwarzschild Mass

Hello guys, I am reading through Wald chapter 6 section 2 on the interior Schwarzschild solution. In it he states that matching the interior solution to the exterior (Schwarzschild) solution gives a Schwarzschild mass of $$M=4\pi\int_0^R \rho(r)r^2 d$$ This would presumably be the same mass...
8. ### PMNS Matrix parameterization

Hi guys, The wikipedia page on the PMNS matrix talks about there being a way to parametrize any 3x3 (special) unitary matrix by 4 parameters: http://en.wikipedia.org/wiki/Pontecorvo%E2%80%93Maki%E2%80%93Nakagawa%E2%80%93Sakata_matrix#Parameterization However, I am quite sure SU(3) has...
9. ### MSW Hamiltonian

Hi guys, I was wondering if anyone knows of a good source/paper that I can find online that details how to derive the MSW Hamiltonian from a field-theoretic approach, or from an effective field theory approach or anything like that? Every time I study the MSW effect, the Hamiltonian...
10. ### Fortran [FORTRAN] Runtime error

Hi guys, I've been tinkering with this code for a while now, as you probably have seen from my other threads. Right now I am working on changing the code around so that it actually writes out the correct output instead of the old output. I am getting this runtime error: At line 2057 of file...
11. ### Fortran [FORTRAN] Assigning bad values in arrays

Hi, I just realized that I have been making bad array assignments in my code. Specifically, I think I have been assigning to slots that the array does not have. For example, I might declare an array: int,parameter :: nflavor=3 int,parameter :: nflavor2=nflavor*2 real,dimension(nflavor)::x...
12. ### Fortran [FORTRAN]Compiler if statements

Hi guys, I'm not really sure what these are called, so I just made a title to the best of my knowledge. I have some questions on some if-statements that I see in some code I'm working with. I will see if-statements like this: #ifdef mpi ... #endif I know that this tells the compiler that if...
13. ### Fortran [Fortran] something very peculiar

Hello guys, As, you probably know by now, I've been trying to run this piece of code for a while now. I finally got it to run and then I realized something very weird is happening! So in my code, which simulates neutrino evolution, I have made 3 conditional statements in the evolution stage of...
14. ### Hard to read code

Hi, is it possible to make the text that is wrapped in [code[ wrappers darker and easier to read? It's so light right now: test Look at this text! It's hard to read! Oh noes!
15. ### Makefile confusion

Hello guys, I am trying to run a pretty substantial piece of code, coded in Fortran. There are many many modules (~10) and the dependencies of one module/piece of code on another is quite complex. As I am not the original author of the code, I am still not intimately familiar with every single...
16. ### Youtube embedding in Chat (shoutbox)

So, since the shoutbox refreshes its page every time a message is entered, an embedded youtube video will also reset when I type something into the shoutbox, making actually watching the video difficult.
17. ### Fortran [Fortran] A piece of code that confuses me

Hello all, There is a subroutine in the code I'm working on that looks like this: subroutine onestep(iter,iegy,icos,jcos,iphi,rinit,rfin, & & v2,v2bar,hel,helbar,drdis, & & psib,psie,psibarb,psibare,err) use params use helectron use angles use neutrinodist use parallel...
18. ### Fortran [Fortran] Functions and naming conventions

Hi guys, In the code I'm working on there are a few functions that will be used to find a Hamiltonian, which I will then use in later parts of the code to find the time evolution of my system. Right now I have it set up so that the function names are actually the names I want to give the...
19. ### LaTeX In-line Latex not working

Is it just me or is in-line Latex not working here anymore? ##\mu,\nu## versus $$\mu,\nu$$
20. ### Avatar image compression

Hi, is the forum compressing my avatar image? I made a 300x300 avatar, and it is very clear (the original resolution is quite high), but on PF it looks very fuzzy. Is there some compression of the file going on? How can I make it not fuzzy? It annoys me -.-
21. ### Icon identifying which treads i've posted in

Is this icon now gone with this new version? I like to know which treads I've contributed in to see if the OP has follow up questions, etc. It makes things a lot easier for me.
22. ### Chat is not working

All day the chat has been a blank white page for me. Is anyone else having this problem?
23. ### Fortran [FORTRAN] Help figuring out zheev

Hello guys, I am in need of a subroutine that diagonalizes a nxn Hermitian matrix (really I'm just looking for the eigenvalues and eigenvectors of course). Looking online I found that LAPACK has a zheev subroutine that presumably does just this. I am a little confused on how to use this...
24. ### Fortran Fortran array declarations

Hi, I'm just wondering real quick, are equations allowed in array declarations? For example: int :: y=2 int, dimension(2*y):: x ?
25. ### Dirac vs Majorana Neutrinos

Hi, I recently attended several lectures on the topic of neutrino astrophysics. I wanted to verify some of the fact that I gleaned for them, specifically about the Dirac vs Majorana nature of neutrinos. 1) The most basic fact first. If a neutrino is Dirac in nature, then it has 3 flavors...
26. ### Log(x) do you assume base 10 or base e?

So, out of curiosity, when you guys see log(x) do you assume base 10 or base e? Because I just wasted 2 hours of my life wondering how I got a problem wrong due to the fact that I assumed base e and the problem assumes base 10...:cry:
27. ### Regarding the Hawking radiation

Hello guys. From my understanding of the Hawking radiation, it is a consequence of QFT in curved space time. The fact that a uniformly accelerated observer sees the Unruh radiation means that by the equivalence principle, a stationary observer at a distance from a black hole will see Hawking...
28. ### Math vs Physics

Which is better? Opinions? I have to say MATH is better. physicS is just so dreadfully boring. most physicists abUse the math anyway. it is Clear that mathematiKS is far superior in any possible way. if all mathematicians would start doing physics, most physical problems would have been solved...
29. ### Particle physics J=L+S

I've never really been...convinced...of the statement $$\bf{J}=\bf{L}+\bf{S}$$ I've always just gone along with it, but I've never seen why this is "right". So I guess now's as good a time as any to ask. Thinking about this from a "classical" perspective (which obviously is not correct, but...
30. ### Path integral Quantum Mechanics

Hi guys, I have a few questions regarding Feynman's formulation of quantum mechanics. Given the propagator K(x',t';x,t), when is this propagator equal to: $$K(x',t';x,t)=Ae^{\frac{i}{\hbar}S_{cl}(x',t';x,t)}$$ Where S_cl is the classical action evaluated along the classical path of motion...