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  1. Ben Wilson

    A Coulomb integrals of spherical Bessel functions

    Hi, I'm no expert in math so I'm struggling with solving these integrals, I believe there's an analytical solution (maybe in http://www.hfa1.physics.msstate.edu/046.pdf). $$V_{1234}=\int_{x=0}^{\infty}\int_{y=0}^{\infty}d^3\pmb{x}d^3\pmb{y}\...
  2. Ben Wilson

    I What mediates the exchange force?

    In many-body theory for electronic structure, fermions experience a force resulting from Pauli Exclusion. So by extension, would quarks and other subatomic fermions experience this force? If so, what is the "high energy" physics side of the story to forces arising from exchange rules? Is it a...
  3. Ben Wilson

    A Castep Setup

    Hi guys, I'm trying to use the CASTEP software for dft calculations. I have plenty of documentation on how to use it once it's all up and running, however I don't know how to get to that point :/ I'm not the best with linux but i've manually installed programs before through tarballs but here...
  4. Ben Wilson

    3D Fourier Transforms?

    Hi, I have a FORTRAN code with an array called Chi that I want to run an inverse FT on. I have defined two spaces X and K which each consist of 3 vectors running across my physical verse and inverse space. My code (If it works??) is extremely slow and inefficient (see below). What is the best...
  5. Ben Wilson

    MATLAB Replace NaN with next element in Multidimensional Array

    I have a a multidimensional array (49x49x49) which has NaN values scattered randomly. For each NaN, I want to replace the value with the previous non NaN value. e.g. if i had a 3 x 3 matrix 4 7 9 2 7 NaN 1 2 NaN should become 4 7 9 2 7 7 1 2 2 I have 3 dimensions [i,j,k], but...
  6. Ben Wilson

    MATLAB Plotting a 3d function

    I had a function of 3 variables f'(kx,ky,kz) and did an ifft f = ifft(f') and now i have a function where inside a small polygon the function f = 1, and outside f=0, within a cube space of length L. how do i plot a scatter graph for this function where there is a point when f =1, and no...
  7. Ben Wilson

    I What is the rotation basis?

    I have a function of a 3 vector, i.e. f(+x,+y,+z) [ or for conveniance f=+++] this function is repeated 4 times where: f1 = + + + f2 = + - + f3 = - - + f4 = - + + I need a formula where i have a different vector for each function in a summation, to obtain the superposition of all 4...
  8. Ben Wilson

    MATLAB Matlab syntax for 2-d fourier transform

    I have a function f(x,y) which i have defined in this way: a vector x and a vector y meshgrid[x,y] z= f(meshgrid[x,y]). how do i do a 2-d fourier transform of f(x,y)? the transform must be done without using operations like fft, and must be done using summations written in the code.
  9. Ben Wilson

    MATLAB Fourier transform of a 2D shape

    I have a function of 2 variables [f(x,y)] where if there was an ellipse in the x-y plane, all values of the function are 1 inside the ellipse and 0 outside. I can plot this function as a surface in 3d where it looks like an elevated ellipse hovering over an elliptical hole in a sheet. My...
  10. Ben Wilson

    I How to word a 3D function?

    I have, say, an ellipse in the x-y plane: (x^2/a^2) + (y^2/b^2) = 1 I want a 3d (e.g. z) function where inside the ellipse z=+1, outside z=0; the function is not continuous. so in effect what I'm left with is a large plane where z= 0, and a small ellipse cut out raised to z=1. How do I write...
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