All Questions
Tagged with cosmology computational-physics
32
questions
2
votes
0
answers
54
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Cosmological numerical computations
I am unsure where to ask this question, whether here or in the Mathematica stackexchange, but either way, I was wondering what are some recommendations for cosmological computations specifically using ...
0
votes
0
answers
18
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Computing matter power spectrum using FFT
I have a 3-dimensional density field from a big N-body simulation, and I would like to compute the matter power spectrum $P(k)$ to see how it compares with the one observed by Planck etc. I know that ...
- 157
2
votes
0
answers
70
views
Initial condition of the millenium simulation
I would like to know the initial conditions used for the millenium simulation. More specifically, I would like to know the amplitude of the initial power spectrum $\mathcal{A}$.
I have found the ...
- 758
1
vote
0
answers
49
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Numerical evolution of Einstein-Boltzmann equations for cold dark matter
I'm trying to numerically evolve the Einstein-Boltzmann equations for cold dark matter perturbations using Runge-Kutta method of the fourth order.
There are 5 standard equations:
\begin{align}
\dot{\...
- 21
1
vote
1
answer
94
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Solve the perturbed Boltzmann Einstein equations in cosmology using RK4 method
I'm trying to learn to numerically solve the perturbed Boltzmann-Einstein equations in cosmology using the RK4 method.
These are the equations:
\begin{align}
\dot{\Theta}_{r,0}+k\Theta_{r,1}&=-\...
- 21
1
vote
1
answer
52
views
Supernovae apparent magnitude in a simplified LCDM model
I want to generate some fake apparent magnitude of supernovae Ia at different redshift using the LCDM model and the fiducial absolute magnitude of supernovae Ia (-19.35) and I want to compare it with ...
- 299
1
vote
0
answers
145
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Smoothing a density field in Python [closed]
I want to smooth a density field. It's represented as a contour plot. The data were given from a 3d array. A smoothed field should be periodic but what I take does not have periodicity. The code I use ...
0
votes
1
answer
55
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Astropy Package - Defining new dark energy parametrization
I was looking through astropy, and I wonder is it possible to define a new dark energy parametrization instead of using the pre-defined ones..? I couldn't see the reference but maybe I missed it.
...
- 3,122
3
votes
1
answer
157
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Cosmology context - MCMC code : Recomputation of covariance matrix after each point accepted
I am working on a MCMC code (basically with Metropolis-Hastings) and I would like to understand different important points.
We always mention the covariance matrix which is used in the computation of ...
user87745
0
votes
1
answer
163
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Numerical solution to the equation of curvature perturbation
Numerical solution to Mukhanov-Sasaki equation
In the above link, an equation is given which is the evolution equation of curvature perturbation as a function of $N$ (number of e-folds). In order to ...
- 21
0
votes
1
answer
693
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How do I convert a .FITS into a numpy array (or a file that can be used in Python)? [closed]
I'm trying to train an AI algorithm to determine photometric redshifts of galaxies, and to do so I have a .FITS file which contains the training data. I need to convert this .FITS file into a format ...
- 11
0
votes
1
answer
123
views
Numerical solution to background equations of cosmology
I am trying to solve the background equations of cosmology numerically using Runge-Kutta Dormand prince method with simplified assumption $8\pi G=1$ and $c=1$. The equations are
$$ \ddot a = -\frac{1}{...
- 31
1
vote
0
answers
82
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Numerical code Friedmann equations [closed]
I have to write a numerical code to solve the ‘Ω-form’ of the Friedmann equation:
H(t)^2/H_0^2 = Ωmat/a^3 + Ωrad/a^4 + Ωk/a^2 + Ωx/a^3(1+w)
...
- 11
0
votes
0
answers
43
views
Numerically solving the equation of motion for inflation in cosmology
So I want to solve the equation of inflation involving a scalar field numerically using python libraries such as odient or scipy. The equation is:
$$\def\phi{\varphi}
\phi''(t)+3H\phi'(t)+V'(\phi(t))=...
2
votes
0
answers
41
views
Why is the boundary of friends-of-friends (FOF) halo corresponding to iso-density contour?
The friends-of-friends algorithm (hereafter FOF) is commonly used to find halos in cosmological simulations. (For more information, please refer to here and here)
I found that some literature argues ...
- 529