# Recent content by Qyzren

1. ### 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. ### 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. ### 4 coupled ode

thanks, problem solved
4. ### 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. ### 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. ### 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. ### 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. ### 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...
9. ### Christoffel Symbols problem in GR

Thank you very much Cristo
10. ### 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. ### 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...