Recent content by birdhen

Hi there, I am having trouble with some Fast Fourier Transforms. I have been using both MATLAB and FFTW in c. The problem is that I want to calculate the potential of a system from the overdensity. The equation in Fourier space is simple phi(k)= -del(k)/(k^2) , where del is the...

Wow, I have just come back to look at this post, thank you for all of your help!

Hi there, I have moved to another computer and can open it fine now. Thanks very much it is very helpful!

HI there, Thank you for your reply, yes, f(T) gravity is an extension of teleparallel gravity. PS I can't get your link to work, it just comes up blank. Cheers

Hi there, I originally posted this in the SR, GR section so sorry for the re-post. Can anyone point me in the direction of any papers that explicitly derive the equations of motion in f(T) gravity. I have seen the wikipedia derivation in f(R) gravity but can't find anything for f(T) where...

Hi, I have been looking all over on the internet and I can't find out how the action is derived. I know it is used to derive the field equations, but why does it look the way it does? Why use the determinant of the metric, where does the 1/(16 pi G) come from? Any help would be great, thanks!

OK , of course, thanks !

Thank you for your reply. I am getting confused still. Would the galactic north pole just have l=0 b=90 in galactic coordinates? I am imagining the surface of a sphere, if b=90 is the top point of the sphere, then there can be no l value as the horizontal plane through the sphere would just be a...

HI there, I am having problems understanding something. If I have an axis pointing towards the galactic north pole, and I rotate it using an Euler rotations how can I can I establish the rotation angles needed so that it will be pointing to the equatorial North pole. I am looking for...

ah, thank you, so y/x=tanφ, and the value of φ will depend on whether x and y are negative or positve. Wonderful, that was the hint I needed, Thank you!

Hi there, I am getting confused about how to work this out. I know that to convert cartesian coordinates to spherical coordinates you can use: theta=arccos(z) phi=arcsin(y/sin(theta)) my problem is that I have a list of coordinates, let's call them THETA and PHI. I change them into X,Y,Z...

Hi there, I am getting confused trying to use fminsearch. I have looked at the help on Matlab but can't seem to understand how to get it to work. I would like to find the minimum chi squared values of two parameters H and omega. I have written a function that will find the min chi squared...

Hi there, I am trying to plot the coordinates of Supernovae onto what I think is known as a hammer plot i.e a 2D plot representing the surface of a sphere. I have no idea how to do this, and have been searching the internet to no avail. Can anyone offer any advice ? I only have a basic...

I think wrote it incorrectly, it would be; (-xe^(-2x^2)) -int(-e^(-2x^2)) -int(e^(-2x^2)), which then cancels.

It is OK I have done it now, I split it into two parts 4x^2(e-2x^2) and -e(-2x^2) and integrated the first part by parts using u'=4xe(-2x^2) and v=x, and then the integral part of the solution canceled with the second part ie the sol'n was ; [-xe(-2x^2)]-int(-e(-2x^2)-int(-e(-2x^2))...