Recent content by Qyzren

  1. Q

    Finding this distribution

    Homework Statement Let X1, X2, ..., Xn be iid random variables with continuous CDF FX and suppose the common mean is E(Xi) = μ. Define random variables Y1, Y2, ..., Yn by Yi = 1 if Xi > μ; 0 if Xi ≤ μ. Find the distribution of ∑ni=1Yi. I'm having a hard time figuring out how to begin to find...
  2. Q

    Parallelised ODE solver

    I wish to solve the following DE numerically on the interval t:[0,a] using parallel processors. Given y'(t)=f(t,y) and y(0)=y0. One way to parallelise the DE is to split the interval [0,a] into n subintervals [ak/n, a(k+1)/n] where k = {0,1,...,n-1}. Problem: I need to know the initial...
  3. Q

    4 coupled ode

    thanks, problem solved
  4. Q

    4 coupled ode

    Hi guys, i have 4-coupled ode's that are giving trouble (1) \frac{dy_1}{dt}=y_2y_3-\mu y_1, \hspace{1cm} \\(2) \frac{dy_2}{dt}=y_1y_4-\mu y_2, \hspace{1cm} \\(3) \frac{dy_3}{dt}=1-y_1y_2, \hspace{1cm} \\(4) \frac{dy_4}{dt}=1-y_1y_2 I need to show that the steady state solutions are y_1=\pm...
  5. Q

    Christoffel symbols

    Thanks, I just did not know it was possible to raise or lower indices for the christoffel symbol. I've figured it out now though
  6. Q

    Christoffel symbols

    I do not understand this "well g_{mk} \Gamma^m_{il}=\Gamma_{kil}" specifically, how you can have a christoffel symbol with 3 lower indices, how does that work? should the 2nd equation not be 0=\frac{\partial{g_il}}{\partial{x^k}}-\Gamma_{lik}-\Gamma_{ilk} instead of...
  7. Q

    Christoffel symbols

    http://en.wikipedia.org/wiki/Christoffel_symbols#Definition start with 0=\frac{\partial g_{ik}}{\partial x^l}-g_{mk}\Gamma^m_{il}-g_{im}\Gamma^m_{kl} in wiki it said "By permuting the indices, and resumming, one can solve explicitly for the Christoffel symbols as a function of the metric...
  8. Q

    Divergence of vector/tensor

    Hi guys, trying to solve a problem in MHD, i realised i need to be able to take the divergence of this following integral, but I don't know how to do it. M is a symmetric rank 2 tensor, r is a vector. The integral is as follows \int_{\partial V} (\textbf{r} d \textbf{S} \cdot...
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    Christoffel Symbols problem in GR

    Thank you very much Cristo
  10. Q

    Christoffel Symbols problem in GR

    Why is it that when I try to solve it using the Lagrangian, my answer is off by a factor of 2 for the c-symbol \Gamma^0_{10} Lagrange's equation for x^0 time component is -\frac{d}{d\sigma}(\frac{\partial L}{\partial(\frac{\partial x^0}{\partial\sigma})})+\frac{\partial L}{\partial x^0}=0...
  11. Q

    Mathematica help

    Hi, not sure where to put this, so i'll just put it here. i was wondering if there is a way to define functions of this sort in mathematica. For example. f(x)=x if x>0 and f(x)=2x if x<=0. I know you can break it up into 2 functions and go something like g[x_]:=x; h[x_]:=2x; but those...
  12. Q

    Question about laplace

    i'm a little bit confused. if the velocity potential Φ = Φ(x,y,t). and it says Φ satifies laplace's equation. does that mean ∂²Φ/∂x² + ∂²Φ/∂y² = 0 or ∂²Φ/∂x² + ∂²Φ/∂y² + ∂²Φ/∂t² = 0. does the time variable get included?? i'm thinking it isn't but i'm not exactly sure.
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    Differential eq (implicit sol)

    Homework Statement i have a differential equation. ∂h/∂t + [g sin a h²/v]∂h/∂x = 0. where h = h(x,t). i need to show by substitution that the (implicit) general solution for h is h = f(x - (g sin a h²t/v)) where f is an arbitrary differential function of a single variable. The Attempt...
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    If it takes me 60 seconds to make a cup of tea, and my manager wants

    if it takes me 60 seconds to make a cup of tea, and my manager wants me to make it 25% faster, does that mean i make it in a) 60/1.25 = 48 seconds b) 60*0.75 = 45 seconds some people say a, some people say b. What do you guys think? I think personally think it's a. If someone told you...
  15. Q

    Astro, p-p process

    part c i've got, directly using E = mc² gives 4.3*10^9 kg but i still have trouble with part b :( Luminosity of sun is 3.826*10^26 W which is 3.826*10^26 J/s 6.55 MeV = 1.049 * 10^-12 protons/J .
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