Questions tagged [computational-physics]
Questions with this tag should be about computational physics, which is the study of physical situations with the use of software (commercial or in-house). Please note that details of writing and/or debugging code is OFF-TOPIC and should be asked at either Computational Science, Code Review or Stack Overflow.
1,808
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How can I use Proper Orthogonal Decomposition on finite element analysis [closed]
Im trying to do Finite Element Analysis using Proper Orthogonal Decomposition (POD), but i cant get force matrix and dont know what result mean.
Let me first describe the process.
1.I analyzed a ...
0
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0
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31
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Textbook recommendation for practical simulation of quantum systems
I'm hoping to find a textbook (or other type of reference) which discusses an introduction to simulating quantum systems with classical computers. To clarify, I'm interested in finding a resource that ...
1
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2
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57
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Numerical resolution of Schrödinger 1D Time Independent Equation, why do Energies not following the expected pattern? [closed]
I want to solve numerically the 1D time independent Schrödinger:
$$-\dfrac{\hbar^2}{2m} \dfrac{d^2 \psi(x)}{dx^2} + V(x)\psi(x) = E\psi(x)$$
For starter, lets say we solve the Particle In a Box ...
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2
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70
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$N$-body gravitation simulation in 2D and 3D
My question is quite general.
I want to make $N$-body simulation, for example galactic dynamics, using $N$ stars.
One possibility is to make these calculations in 2D using an inverse square law and ...
0
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0
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30
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Admissible solutions for waves propagating in a fluid medium obtained from Fast Fourier Transform
Given a two-dimensional pressure distribution $p(x,y)$ in a fluid medium, we can perform Fast Fourier transform to obtain the amplitude and phase spectra. The 2D-FFT (and eventually, the IFFT) ...
2
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0
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87
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Numerical Relativity for Computer Scientists
What resources on numerical relativity/simulation would be suitable for a primarily theoretical computer science background [algorithms analysis, complexity theory, etc.]? Importantly, while I'm ...
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43
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How to properly discretize and solve the Liouville equation?
Consider some dynamical system $\dot{\textbf{X}}(\textbf{x},t)=F(\textbf{X})$ where $\textbf{X}$ is discretized along a 1-dimensional spatial coordinate $\textbf{x}=(x_1,\dots,x_N)^T$. Let $\rho(\...
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47
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Can we project into Pauli size sectors efficiently?
Suppose that we have a system of $L$ qubits and some Hermitian operator $\mathcal{O}$ acting on the system. We can expand $\mathcal{O}$ in Pauli strings $P_{n}$:
$$\mathcal{O} = \sum_{n=0}^{4^{L}}c_{n}...
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0
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29
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Is Quantum State Tomography (QST) an inherently supervised or unsupervised problem in Machine Learning?
I am studying how to apply neural networks to the problem of Quantum State Tomography (QST) and I got confused when it comes to decide if this is a supervised or unsupervised learning problem.
At ...
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1
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39
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Quantum oracle for boolean function
As a math student, I am doing some quantum computing. In the course notes of Ronald de Wolf, he says that any Boolean function $$f:\{0,1\}^n\to\{0,1\}^m$$ can be made into a unitary operation that ...
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Transition boundary condition
I am reading about the "Transition Boundary Condition" at this link.
Can someone please explain where the following boundary conditions come from?
$$J_{s1} = \frac{Z_s E_{t1} - Z_T E_{t2}}{...
2
votes
2
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121
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In general relativity vizualizations what are the equations of grids?
I am wondering what curved 3D grids in GR outreach correspond to in equations. How would I compute such a curved grid if I know the metric tensor $g_{\mu\nu}$ in every point of space? What would be ...
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23
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How to model the vacuum-solid interface?
Consider an ordinary object, e.g. metal or an insulator placed in a simulation mesh to simulate a CFD physics problem, creating a solid-vacuum interface. I cannot model this as a dense ideal gas as it ...
0
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2
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98
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Simulating the helium atom using the Schrödinger equation numerically?
I recently set up a numeric solver of the Schrödinger equation and can receive solutions for single-particle quantum mechanical problems. I became interested in simulating atoms, since there is a ...
0
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0
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Why the energy of light in a photonic structure ≠ the energy of its equivalent circuit model generated by EIFE?
For simplicity, we suppose $\epsilon_0=\mu_0=1$ and that the photonic structure is only made of perfect metal and vacuum.
The electric field and the current density are related by the Green's function,...
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0
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23
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Calculating interclass and intraclass correlation coefficients - using SPSS or Excel [closed]
For some context, I do biomedical science and dont have a strong background in physics or stats even. For my research project, im measuring different parts of bones, including widths, volumes and ...
0
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1
answer
32
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Determining star position and velocity to deduce closest approach?
I am trying to replicate the results found for Gliese 710's closest approach of ~0.05 parsecs in 1.3 million years approximately. I thought that by plotting the sun at (0,0) and using the stars ra,dec,...
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0
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11
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Interpreting the van der Waals Energy Discrepancy between $\rm MoS_2$ and Graphene Layers in Computational Simulations
I am conducting computational simulation tests and have observed that when simulating systems like molybdenum disulfide ($\rm MoS_2$), the interaction between layers (S-S interaction) is quite strong, ...
0
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0
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25
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Evaluate convergence of force constants in crystal with increasing cutoff
I have a crystal with 2 atomic species, A and B. I'm interested in the interatomic force constants (IFCs) and I have a program that computes them for a given supercell. Basically, I have to provide ...
0
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1
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78
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Sublattice model for ternary system
Much like in an earlier post of mine, I'm now calculating the phase diagram
of a ternary system (Ag-Al-Cu, to be specific), which has some phases modelled as sublattices (using this publication for ...
1
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1
answer
78
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Off-Axis magnetic field ($B_z$ @ $\rho=0.5 R$) of a finite solenoid
I am doing mathematical modelling in MS Excel Spreadsheet for axial magnetic field (Bz) at different distances away from the centre for a finite model. I see small hump at the fringe (i.e. just ...
0
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0
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47
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Use of Binder Cumulant for Determining Critical Temperature
I am completing a computational project where I am simulating the Ising model using Monte Carlo methods, namely the Metropolis-Hastings algorithm, and the Wolff algorithm.
For the Metropolis-Hastings ...
1
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1
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48
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Euclidean LQCD not on a lattice?
How much the idea of calculating Euclidean path integrals in LQCD is fundamentally tied to using formulations based on the discretized spacetime lattice?
In computational approaches to quantum many-...
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0
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46
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Intertial finite-size effects in fluid simulations
A gradient $\nabla \rho$ in the density field $\rho$ of fluids at thermodynamic equilibrium is suppressed at a rate given by $D \nabla^{2} \rho$, allowing to measure the diffusivity $D$ of the fluid ...
0
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1
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52
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How optimal launching angle is affected by mass?
I'm writing a code to calculate the maximum optimal angle for motion under linear drag and how it's affected by mass. It appears that for the most part this angle is independent of mass and not of ...
1
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0
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50
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Brightness of the light source at twilight computation
I would like to determine the brightness of the light source at twilight based upon its apparent magnitude.
In the question here:
What are the average wavelengths and brightnesses of sunlight across ...
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0
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34
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Need help in Debugging Fourth-order Runge-Kutta for a differential equation in Python [migrated]
I have been trying to solve this differential equation using Runge Kutta method on Python and have been stuck on it for days now. I haven't been able to get the right result with the code I wrote. ...
0
votes
1
answer
60
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Math and Pseudo code paper on black hole binary simulation
I want to do a short practice to see how mass evolve space and how space curvature evolve mass distribution.
Most of the GR simulations were rather complicated but I think the black hole binary had ...
0
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0
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15
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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 ...
0
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1
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53
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Prime operator for sinusoidal testing function in self-term approximation for Thin Wire using Method of Moments (MoM) $s_m^{'}(x_p)$?
I am implementing thin wire method of moments using W.Gibson's "Method of Moments in Electromagnetics". The approximation for self-term using piecewise sinusoidal basis function is given as
...
2
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1
answer
53
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Is it possible to solve numerically the classical Yang-Mills for a generic source?
The classical Yang-Mills equation in the presence of a source $J^\nu(x)$ can be written as
$$
\partial_\mu F^{\mu \nu} - i g [A_\mu, F^{\mu \nu}] = J^\nu (x),
$$
where $F^{\mu \nu} = \partial^\mu A^\...
1
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1
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Understanding the left-canonical matrix product state
I am trying to understand how to represent any quantum state as an MPS while working through this review by Schollwöck. My goal is to take any random $2^N$ dimensional vector and construct its MPS ...
1
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1
answer
60
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How small is $\eta$ when we say $\eta\to 0^+$ in Green's functions
When we convert Matsubara's imaginary time Green's function to the retarded Green's function, we perform an analytical continuation by substituting $i\omega_n$ with $\omega + i\eta$, with $\eta\to0^+$....
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42
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Inverting a bubble interface to recover the level set function
I have access to some high quality CFD data that includes 2D and 3D level set functions for simulations of bubbles. Masking the level set function using a heaviside is easy and it is a fast way to get ...
0
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1
answer
65
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Special relativity velocity addition formula precision [closed]
I tested the special relativity addition formula
$$u_{\text{total}}=\frac{v+u}{1+\frac{vu}{c^2}}$$
and
found that addition of small numbers converges to smaller speed, but bigger numbers to bigger ...
2
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0
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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 ...
0
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0
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42
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Finding the bound state energies in the MIT bag model numerically for a general bag shape
The MIT Bag Model is a simple model used to describe the properties of bound quarks in Hadrons, without considering the strong interaction between the quarks with the following boundary condition
$$(1+...
0
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1
answer
78
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How to calculate mean squared displacement (MSD) value as function of Tau (lag-time)
I'm doing a research on Brownian motion (in 2D) and I want to calculate the MSD values in order to find the diffusion coefficient $D$.
However, online I find different approaches on how to calculate ...
1
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2
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156
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Point load distribution inside elastic solid continuum medium in finite elements method
In finite elements method, when point load is applied to a particular node of elastic solid continuum medium (e.g. soil), does it affect nodal forces in the rest of the mesh (i.e. does each node ...
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0
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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{\...
1
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0
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44
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Electromagnetic fields in voltage biased conducting strip
Consider a conducting rectangular strip of length $L$ (along x-axis) and width $W$ (along y-axis), with a potential difference (rather EMF $\int E.dx$) V(t) applied. We can assume that V(t) changes ...
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Understanding chapter 3.1 (Laplace's equation) in Introduction to electrodynamics Griffiths 4 ed [duplicate]
I really need help to understand chapter 3.1.
What is the method of relaxation?
How can I use the method of relaxation to solve Laplace's equation?
How can I use the first and second uniqueness ...
0
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0
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53
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Regarding Metropolis-Hasting Algorithm
This is motivated by this post Metropolis-Hastings and underlying Markov process. I am also trying to compute the stationary state of the Boltzman distribution by the method discussed in the post. ...
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0
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Limit of solving the 1D Heisenberg chain to find the dynamics numerically
I am trying to simulate the dynamics of a 1D Heisenberg chain using Python.
I am going step-by-step.
There is an external magnetic field along +Z direction.
At first we consider a single classical ...
2
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0
answers
51
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Frequency Response of a Stochastic Oscillator Numerically
I am willing to obtain a frequency response plot for a stochastic oscillator governed by the following equation numerically.
$$
\ddot{x}+2\Gamma \dot{x}+\omega_{0}^{2}x=f(t)
$$
where $f(t)$ is a ...
0
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1
answer
42
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Calculating Scattering matrix of a nuclear fusion reaction using Fortran
I am trying to find out the $S$-matrix elements for the reaction:
$${}^{19}\textrm{F} + {}^{208}\textrm{Pb}. $$
The model followed is Direct reaction model where the optical potential is:
$$ V_{op}(r) ...
2
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0
answers
39
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Hydrodynamic interactions and finite-size corrections
In molecular dynamics simulations of fluids it is known that diffusion coefficient $D$ of fluid simulated under periodic boundary conditions in a cubic box with size $L$ decays with a factor $\frac{1}{...
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78
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Setting up a wall with a slit inside the domain of a 2D wave being solved using the fourier-spectral method
The wave equation is given by:
$$ \frac{\partial^2 u}{\partial t^2} = \alpha^2 \cdot \left( \frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} \right)$$
If we assume the solution to ...
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0
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Free energy as a function of temperature over phase transition in molecular dynamics simulation
I've constructed a low density standard MD simulation (in Python), using the Lennard-Jones potential with an Andersen thermostat, of 10 particles in a box V = 10 $\times$ 10 $ \times$ 10 in the NVT ...
2
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0
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How non-local can the interactions be for Density Matrix Renormalization Group (DMRG) to still work?
I know that Density Matrix Renormalization Group (DMRG) / Tensor Networks (TN) work well for local Hamiltonians, where on each site I have a fermion or boson, which only have nearest-neighbor ...