All Questions
Tagged with numerics or computational-physics
1,932 questions
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More accessible definition of Galerkin methods for poisson equation [migrated]
Galerkin methods are used in solving Poisson equation. Is there any pedagogical and more basic explanation of the method?
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72
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Recent machine learning/AI by-for physicists
I am looking for a recent (no more than 6 months or so in arXiv) review of machine and/or deep learning developments for physicist written by physicists, preferably with material and discussions about ...
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26
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How to find electro-thermal analysis of an arbitrary shape of conductor? [closed]
I have an arbitrary shape of conductor in a step file. I would first like to find the resistance of said conductor and then observe the change in resistance due to change in temperature. I do not have ...
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33
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40
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Particle-mesh method & energy conservation [closed]
Disclaimer: I'm a complete novice when it comes to computational physics but I want to learn more. As a starting point, I wanted to implement the particle-mesh method following Hockney's textbook ...
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18
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How to minimize the Helmholtz energy functional by picard iteration? [closed]
As far as I know, the picard iteration is for ODEs. I wander how such method works in the minimization of Helmholtz energy functional derivative which is core part of classical density functional ...
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I'm doing my project work on astrophysics. So what i want to find how much black hole grows over time
So problem in the code I have to find the velocity of gas that falling in the black hole at the point of event horizon,from this i can find the increasing $dm$ mass from Bondi equation over $dt$ time. ...
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1
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25
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Phase field of a vortex anti-vortex pair
I am just wondering if we have a vortex anti-vortex pair, what does the over all phase field look like?
I know they interact via their winding numbers, and the pair is more stable than the ...
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44
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Eigenvalues of Cooper Pair Box with Matlab
I wanted to evaluate the eigenvalues of the Cooper Pair Box Hamiltonian in number basis
$$
\hat H=\sum_n 4E_c(n-n_g)^2 |n\rangle\langle n|-E_J/2(|n\rangle\langle n+1|+|n+1\rangle\langle n|)
$$
as a ...
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17
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FeynRules error [migrated]
I am trying to run a simple FeynRules calculation for a simple qed lagrangian. But I am getting errors. FeynRules don't have documentation of errors. The errors are:
PartClass::NoGenMatch: Number of ...
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32
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WKB tunneling probability calculations
I'd like to calculate the WKB tunnelling probabilities from different vibrational levels. I hope the question is not too chemical.
I have a compound which undergoes a chemical reaction. For the ...
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167
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Computation of conformal Hubble parameter
I'm trying to calculate the conformal Hubble parameter $\mathcal H$ using Astropy, but I'm unsure about the correct approach. I know that the standard Hubble parameter $H(t)$ is related to the scale ...
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33
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How to define an equitable success event in quantum-walk-based multiple-targets search algorithm?
In quantum search algorithms (on a 2D grid or other setting), when there are multiple targets, a "successful search" event is often defined in following:
$$P_{success}=\max_{t\in [0,T]} \...
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86
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How to Invert Dispersion Relation $\epsilon_k=2t[\cos(k_x a) + \cos(k_y a)]$ to Solve for Wavevectors $k_x$ and $k_y$ in Terms of Energy $\epsilon_k$?
I am working on a problem related to the dispersion relation of electrons in a 2D square lattice with nearest-neighbor hopping. The energy $\epsilon_k$ is given by:
$
\epsilon_k = 2t [\cos(k_x a) + \...
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41
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Gerchberg-Saxton algorithm noisy phase retrieval
I am trying to reconstruct a phase-only diffraction grating that produces $n$ beams of equal intensity.
Specifically, I am trying to reconstruct a 9-beam phase profile with the following form:
$$ \phi(...
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38
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Using Gaussian decomposition in numerical algorithm for 1D Schrodinger equation
I've been working on this as a small hobby side project to my main graduate work in a different area, so please excuse any lack of knowledge.
I've been developing a program for simulating an arbitrary ...
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1
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Linearized or nonlinear least squares for Arrhenius: mitigating heteroscedasticity
I have a question that is essentially expanding on this older question, but digging into a specific aspect of it that was not directly discussed
Suppose I have data points that fit an Arrhenius trend:
...
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1
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58
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Problem solving geodesic equations numerically [closed]
I been having trouble solving the geodesic equations. The end goal is to plot them on a surface. I firstly calculated the Christoffel symbols and then inserted the differential equation in an ODE ...
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72
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Best way to calculate velocity, acceleration and jerk with different temporal resolutions
I have body motion tracking data I am using for my thesis. I am trying to find relationships between the kinematics of the body of speakers, and the acoustic measures of their speech (e.g. speech ...
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Constructing Embedding Diagram of Reissner-Nordstrom Dihole [closed]
Is it possible to create embedding diagrams of $\phi=constant$ slices of axisymmetric two black home spacetimes, like the Reissner-Nordstrom dihole?
$d\Sigma^2=U(x,y)^2(dx^2+dy^2)$
I ask because the ...
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Plotting polarization of EM waves in Matlab [closed]
There is a polarization matrix I want to implement in Matlab.
I have built a basic Matlab plot which could visualize EM waves in 3D.
The basic equations described in equation $(2.5.1)$ from the ...
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1
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49
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How to understand the non-linear calculation model of demagnetization curve correctly?
in the doc of MotorCAD, I found that the demagnetization curve can be calculated by like this non linear model:
In above formula, the Br at specific temperature can be calculated like this:
And the ...
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103
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Other than DMRG, what's the advantage of representing operator in MPO form?
I have been working with density matrix renormalization group (DMRG) (which a numerical method based on tensor network to find ground state energy), but I don't really get that, other than doing DMRG, ...
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33
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Insertion operation bias in Grand Canonical Monte Carlo (GCMC) simulation software
I'm working on my own Grand Canonical Monte Carlo (GCMC) simulation software. The insertion operation, where an absorbate atom (e.g. hydrogen) is inserted in the system at a random position, is ...
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71
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Is it possible to derive an initial value for a field or have I reached a numerical limit?
The effective potential of the Higgs field can be written in the form: $$V_{e} = \frac{M^2(T)}{2} \phi^2 - ET \phi^3 + \frac{\lambda_0}{4}\phi^4$$
We can parameterise this using $\phi = \frac{M^2}{...
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1
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57
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Finite difference scheme for solving 3D stationary diffusion equation in inhomogeneous medium using spatially irregular orthogonal discretisation grid
I try to numerically solve the 3D stationary diffusion equation in a medium with spatially inhomogeneous conduction.
Analytical problem
In the context of this post, heat diffusion is considered. The ...
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29
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What is the correct way of implementing density matrix renormalization group (DMRG)?
I am a new comer in DMRG. I want to learn doing some simple DMRG. I come from the community of Hartree-Fock and exact diagonalization. I have a few questions on DMRG:
(1) The classical starting review ...
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Verifying Hooke's law through video analysis in a dynamic setup
For educational purposes, I am attempting to experimentally verify Hooke's Law using a dynamic setup analyzed through video footage. In this experiment, a body of mass $m$ is accelerated by a spring. ...
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What techniques are available to solve this 2nd-order ODE?
In Toward the Theory Of the Electroweak Phase Transition by Dine, Leigh, et. al they solve the 2nd-order ODE:
but I can't undestand how they have approximated an answer here? Both Laplace transforms ...
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2
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112
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How do I simulate and control a 3DOF Inverted Pendulum?
I'm working on a project that involves controlling a 3DOF (latitude, longitude, roll) inverted Pendulum with Thruster (see image for a simplified sketch). The Thrusters will apply impulses onto the ...
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35
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Difficulty fitting a curve with many parameters in SciPy [closed]
I am trying to fit a curve to some data points, however the fit is not as good as I'd like. The function I am fitting too is a ZBL type screened coulomb potential.
This is my code:
...
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65
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Can a universe-sized computer predict the universe? [duplicate]
I'm not asking about a simulation and so I don't see this as a duplicate, and I'm not a physicist or anything like that, I have some physics-related questions though.
Current models suggest local ...
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Help with solving multiphoton and avalanche ionization rate equation of fused silica [closed]
I am trying to solve a rate equation that describes the evolution of free electron density of fused silica under action of a Gaussian Beam with peak intensity of $100 \,\text{TW}/\text{cm}^2$, pulse ...
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34
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How can I determine the number of harmonics for this case? [closed]
I would like to comment here on a question I have regarding an analysis of an experiment I must present and I thought I could find some answers here to certain problems I'm having.
In short, I am ...
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Smoke simulations and how to render them
I recently began a real time smoke simulation system, and I need some help with the rendering. I didnt know if to ask here or on the game development stack exchange, but I decided here as it is ...
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38
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Calculation of boson number density using Bose-Einstein statistics
I need help with the Bose-Einstein statistics for calculating the boson number density. I am trying to perform the calculations for a given chemical potential, $\mu>0$, and I want to integrate from ...
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1
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50
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Resolving angular components for collision between two 2D rigid circles
I am trying to make a simple 2D physics simulation where many different 2D balls move around and collide with each other. Currently, I am able to resolve their collision for translational motion (i.e....
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How to determine the alpha value of artificial viscosity in smoothed particle hydrodynamics?
I am confused about how to choose an appropriate value of $\alpha$ in the artificial viscosity. The value that I deduced is far from the recommended value and led to great numerical instability.
...
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60
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Are there quantum computing algorithms specialized for machine learning applications?
I've heard that some companies are attempting to utilize quantum computing algorithms for machine learning tasks (ex:protein folding and drug discovery). As far as I know, quantum computing has been ...
1
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1
answer
480
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Doubt in Verlet's Algorithm
In studying the temporal evolution of a system according to the deterministic model, we begin by considering a Taylor series expansion for the displacement $r$. First, we consider a positive variation ...
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How do I interpret the discrete Laplacian being an approximation of the Hessian (Force Constant) matrix?
Mathematically, the discrete Laplacian is equivalent to the trace of the Hessian. I've read in my literature review that the Force Constant Matrix (FCM) of a lattice system, which is a Hessian matrix, ...
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1
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Numerical relativity and spin weighted spherical harmonics of spin -2
Why do the polarization modes of gravitational waves get expanded into spin weighted spherical harmonics of spin -2 for numerical simulations?
For example in this paper of the sxs catalogue they do ...
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Writing a code to generalise making Real Space Hamiltonian Matrices for a Graphene Lattice
Background
So I've been working on making Hamiltonian Matrices for a graphene lattice and till now we've been working manually, I've attached a picture showing the matrices for a 2 by 2 Graphene ...
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Within traditional DMRG, how do I calculate a reduced density matrix?
At every step of traditional DMRG (one that does not involve tensor networks), one truncates the entanglement spectrum an uses the truncated Hilbert space to add new sites. This prevents the ...
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2
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176
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Neglected Term in the energy gradient for Variational Monte-Carlo
I'm looking into variational Monte-Carlo to determine the optimal variational parameter that corresponds to the ground state of a Hamiltonian. In general I am interested in tight binding models where ...
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42
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What is the relationship between electron-phonon coupling and nonadiabatic effects?
We know that under the Born-Oppenheimer (BO) approximation, the motion of nuclei and electrons is decoupled. However, when there is a degeneracy between potential energy surfaces, the nonadiabatic ...
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2
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674
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How can I calculate derivative of eigenstates numerically?
I want to calculate $\langle n | \partial_{k_x} n \rangle$ where $| n \rangle \equiv | u_{n,\mathbf{k}} \rangle $ is the $n$-th Bloch eigenstate of a $6\times6$ Hamiltonian $H\equiv H(\mathbf{k})$. ...
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Interpretation of fourier transform of a specific time serie
I have two time series from an accelerometer attached to two different factory machines with the hope of picking up subtle differences between the machines and being able to tell when a machine should ...
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Calculate MPS tensor for a given translationally invariant state (numerically)
Assume you are given a many-body state that lives on a 1D chain with local Hilbertspace dimension $d$ on each site and length $N$ as a vector $|\psi \rangle\in \mathbb{C}^{d^N}$. Let the state be ...
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Symmetry and integrability in classical Hamiltonian
I am trying to understand the behaviour of an Hamiltonian system I'm simulating. I will give a quick context setting. The system is defined as
$$
\mathcal{H}(\mathbf{z};\mathbf{z}^*) = \sum_{i=1}^{M}...
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