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.

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Why does this appear in my program when running it? [closed]

I am making a plasmon simulation program using the Meep library, when I run the code everything goes well until it stops running and kills comes out. I do not understand, why.
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Is $φ_P$ equal to $φ_E$ with no diffusion and only convection in the discretisation scheme?

I'm now studying the transportiveness of discretisation schemes using An introduction to Computational Fluid Dynamics: The finite Volume Method; HK Versteeg & W Malalasekera; 1995. In Page 144 it ...
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Is there a fundamental limit to the precision of calculations?

For daily applications, it is accepted that there are limitations to the precision of our calculations when we want to compute quantities that are rational multiples of irrational numbers. Then ...
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Good Calculators for small numbers [closed]

I know this is probably a stupid question, but I honestly cannot find one I am looking for online. Does anyone know of any calculators that can handle multiple calculations at very small numbers (on ...
1 vote
2 answers
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How to correct for collision in $N$-dimensional bounded motion of a particle? [closed]

I want to numerically simulate the motion of a particle (unit mass) in $N$-dimensional space according to the force $f(\vec{x})$ and bounded by a set of linear constraints (equalities as well as ...
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Winding Number with periodic boundary conditions (PBC)?

Imagine we have a SC with a vortex of winding number 1 (one flux quanta) described by: $\theta(x,y)$. If we look at a BdG-Hamiltonian with periodic boundary conditions (PBC), it is easy to write down ...
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How do you solve any partial differential equation using equivalent circuits? How is this possible?

Here's the quote from this wiki: In 1945 Kron suggested an approach to Schrödinger's equation with networks. The same year he used equivalent circuits to solve differential equations. So I've been ...
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1 answer
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Plot Nusselt number between two plates [closed]

I have a free convection system between two walls (hot, and cold). And I have the temperature distribution between them, solved numerically. Now I need to plot the Nusselt number between walls. This ...
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Simulating Arbitrary Superpositions of Quantum Dot Wave Functions

I'm looking for a relatively easy-to-use software like this or this that allows me to calculate and visualize the shape of arbitrary position-space wave functions in a quantum dot/quantum well. I like ...
3 votes
3 answers
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Methods in Numerical Relativity

I have been reading the book of Masaru Shibata Numerical Relativity to grasp some ideas on the methods used. I see that at the heart of the method the system of differential equations is "...
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Calculating entanglement negativity without constructing density matrix

There are two procedures that I know of for finding the von Neumann entanglement entropy of a bipartite system split between $A$ and $B$ - a bad way and a better way. I have in mind computationally ...
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Sensor Array Position Calibration in Anisotropic Media

Problem. I have a sensor array consisting of $n \gg 4$ receivers at unknown locations $\langle x_n, y_n, z_n\rangle$ embedded in an anisotropic medium whose index of refraction varies as a known ...
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Does the resolution of a timeseries affect the estimate of the power-spectrum?

I have been trying to estimate the power spectrum of a timeseries using fourier transform. I noticed that by downsampling my timeseries I get a different spectrum as shown below Here you can see ...
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Integrating Langevin Dynamics equations in computer simulation

In a Langevin Dynamics simulation the following equation is solved numerically : $$ m_i\frac{d^2r_i}{dt^2}=F_{int}-\gamma\frac{dr_i}{dt}+R(t)$$ $$\langle R(t)\rangle=0 \quad \quad \langle R(t)R(t')\...
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Band Structure of Graphene from Exact Diagonalization of Finite Lattice

Say I write down a real space matrix Hamiltonian for a finite graphene lattice, perhaps a rectangle with N sites along each axis. Of course if I had an infinite lattice then I can use Bloch's theorem ...
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Research Areas which combine Computer Science with Physics? [closed]

Throughout my high school i loved physics very very much. I always wanted to a PhD in physics. Along with i thought of pursuing space science. But due certain reasons i ended up in Computer Science. I ...
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Is there a powerful interactive tool for visualizing Lorentz transformations of worldlines?

This Geogebra demonstration is pretty amazing for obtaining a more intuitive understanding of Lorentz transformations. However, it has its limitations. If it would allow the user to add worldines and ...
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Converting Matrix Product State (MPS) to State Vector

Given MPS representation of a state vector with respect to some basis, how can we go from MPS representation to state vector representation?
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First order and second order phase transition in signal recovery

Warning: I'm a computer scientist and my understanding about physics is very limited Recently I came across the term first-order phase transition in a paper where we try to recover a signal $x$ from $...
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1 answer
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Why Matrix Product State (MPS) representation provide fast computation?

I am interested in tensor networks and I am trying to understand why MPS (for example) provide an efficient representation of a quantum state. In order to transform the quantum state in MPS ...
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1 answer
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Stopping too soon [closed]

I have an object going $1000\frac ms$, $vi$, that I want to slow down to $250 \frac ms$, $vf$. I want it to slow down in $10000m$, $d$. I want to know how much deceleration is necessary, and how long ...
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1 answer
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Problem in code for Monte Carlo method for frustrated Ising model

I'm studying Monte Carlo method (it's related to my school project). The code I'm using I got from a paper by Jacques Kotze (https://arxiv.org/abs/0803.0217). In his paper, he uses the Monte Carlo ...
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How does Temperature work in particle-based simulations?

I've seen a number of particle based simulations of things like magnets settling or crystaline structure forming or other phase transitions assosciated with temperature. I can kind of accept that an ...
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1 answer
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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. ...
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1 answer
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Langevin Dynamics simulation at different values of friction coefficient

I am a beginner in the area of Langevin Dynamics simulation. The following equation is solved numerically: $m_i\frac{d^2r_i}{dt^2}=F_{int}-\gamma\frac{dr_i}{dt}+R(t)$ In Langevin Dynamics simulation ...
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2 answers
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Numerical Computation of Electrostatic Field Lines

After solving for the potential $V(x,y)$ from a Laplace Equation $\nabla^2V=0$ in a closed 2D domain, I can readily compute the isopotential lines $V(x,y)=V_0$ with $V_0=0$ to $1$, and the Electric ...
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Why numerical solution of hydrogen Schrodinger equation diverged in higher energy levels?

I am studying Computational Physics by Thijssen. I also read this notebook https://github.com/tamuhey/python_1d_dft/blob/master/numpy_1ddft.ipynb. Then I changed this notebook to solve this ...
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1 vote
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Finding the initial conditions of a conservation law hyperbolic system? [closed]

Consider $u(\boldsymbol{x},t)$ to be a function that is known at $t=0 $ by the initial conditions $$u(\boldsymbol{x},0)= f(\boldsymbol{x}),\quad u_t(\boldsymbol{x},0)= g(\boldsymbol{x})$$ Where $\...
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What does it mean by "scale mismatch" and "bridging of scales"?

As far as I understood, molecular simulation works in two types of scales: temporal scale - how much time is required to simulate the model. spatial scale - how much memory-space is required to ...
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1 answer
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Rationale behind the Variational Monte Carlo Method

The variational method can be used to calculate the ground state wavefunction of a quantum many-body system. Suppose we have a trial wavefunction representing the ground state of the system, ...
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Best computational method for describing the electronic configuration of an ion in a crystal structure

I have a question to ask you: does anyone know an accurate computational method to calculate the splitting of the d and/or f orbitals of a type of ions that are part of an ionic crystal? For example: ...
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Normalization-Formula for contracted Gaussian Orbitals

I am trying to write a python script that implements the Hartree-Fock-Routine. I am currently working on generating the basis-functions. While doing my research I found this website that explains how ...
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1 answer
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Does SXS catalog for NR simulations have non-spinning, non-eccentric blackholes?

I am looking for NR waveform for two non-spinning and non-eccentric black hole binary merger for small mass ratio. Somehow, on the SXS catalog website, I don't see any such description. Thanks
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Closure conditions in the form of equation of state

While reading the book "Riemann solvers and numerical methods for fluid dynamics" By E. Toro, the very first paragraph is: "In this chapter, we present the governing equations for the ...
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Depression in central peak of real part of diffusing Gaussian

I'm attempting to use Crank-Nicolson scheme to solve the TDSE in 1D. The initial wave is a real Gaussian that has been normalised. As the solution evolves, a depression grows in the central peak of ...
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How to normalize cartesian gaussian type basis sets?

I am currently working on my graduation paper each high school student in Switzerland has to write. I chose quantum mechanics. To be more specific Hartree-Fock-Theory. I understand all the theory ...
-1 votes
2 answers
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Generalize knowing when to accelerate towards or away from a target you are moving towards to arrive without overshooting it

Imagine you are a spacecraft moving towards a position and you start out with zero relative velocity. You accelerate towards it, then halfway there you start accelerating in the opposite direction so ...
2 votes
0 answers
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Dynamical system model representation for the geometric motion of soap bubbles

I have been trying to describe the dynamical system model for soap bubbles proliferating, coming into existence and moving and pushing around other bubbles (i.e. water gushing into a sink, full of ...
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1 answer
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What is cocktail MC sample in physics analysis?

In high energy physics, when scientists make a physics analysis, sometimes they use cocktail Monte Carlo sample to study signal and background shape. But I just know what inclusive or exclusive MC ...
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1 answer
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How should I set the boundary condition of a diffuse equation in a potential well?

I want to solve the initial value problem of a particle diffusing in a well on a disk. Paticle density$\rho(\vec{r},t)$satisfy the following equation: $$ \partial\rho/\partial t=\nabla\cdot(\nabla V(r)...
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How to numerically simulate random quantum circuit?

Recent years, measurement induced phase transition has been widely studied with random quantum circuit model https://journals.aps.org/prx/abstract/10.1103/PhysRevX.7.031016 . I know little about ...
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Getting top-of-atmosphere (TOA) irradiance from Bird solar model

I'm just getting acquainted with the Bird solar irradiance model after finding via pvlib-python. From skimming the references, it looks like the Bird model does generate spectral atmospheric ...
2 votes
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Question about the MATLAB gravity models

There is a graph showing the gravity values as a function of latitudes for point mass, zonal harmonic, and wgs84 gravity models at Comparing Zonal Harmonic Gravity Model to Other Gravity Models. The ...
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4 votes
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Why is my simple RK4 failing to capture adequate spring deformation?

I am setting up a very simple physical model for two colliding particles modeled as elastic spring's obeying Hooke's law. I have set up a numerical model for the collision and while the end stages of ...
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1 answer
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The use of Principal Component Analysis (PCA) in Spectroscopy [closed]

Greetings there fellow users. I am to prepare and give a seminar on Principal Component Analysis (PCA) in the subject of Laser Spectroscopy (aka solid state spectroscopy). Now i am quite comfortable ...
1 vote
1 answer
103 views

Problem solving (numerically) the Tolman-Oppenheimer-Volkov (TOV) equations for any equation of state [closed]

I've been working on a code to solve the TOV equations for a while and recently I've got it right but only for one specific equation of state, the bag model, wich is not what I need since it should ...
0 votes
1 answer
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Equivariance and Wigner $D$ matrices for Spherical harmonic rotations

I am trying to understand equivariance in machine learning, specially as discussed in the following paper. Claim is that equivariance is when Group symmetry operation, such as rotation, commutes with ...
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1 answer
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How to set mask size when apply inverse-FFT to the power spectrum of HAADF-STEM image?

Hello everyone, I want to characterize dislocation in my FIB sample using Titan electron transmission microscopy and I want to use FFT filter to process my HAADF-STEM image with DigitalMicrograph (...
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How to apply a Stokes-law type drag correlation to simulate particle transport?

I am implementing a model to simulate the (two-way coupled) transport of particles in a fluid. The flow field is being solved by a numerical solver for the Navier-Stokes equations (in this case using ...
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Reshaping $U$ and $V^\dagger$ matrices resulting from an SVD into rank-3 tensors

Let's say, that we have a $6 \times 6$ matrix $M$. By conducting an SVD of $M$ we obtain $USV^\dagger$ matrices, where $U$ is of size $6 \times 6$ and is left-normalized, $S$ is diagonal with 6 ...

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