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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6
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1answer
240 views

Avoid the singularity of Coulomb matrix elements in grid-based calculations

Whenever one is doing grid-based calculations for particles interacting via the Coulomb potential, the singularity of the Coulomb potential $w(\mathbf r_1,\mathbf r_2) = \frac1{|\mathbf r_1 - \mathbf ...
6
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1answer
146 views

Calculating distribution of force in a N-body system of balls

With three balls placed in a pyramid on a static ground and under the influence of gravity, how will the force of gravity be distributed? The balls have different radius and mass. The initial velocity ...
6
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1answer
288 views

Quantum tunneling probability for a 3d potential

I have an electron potential energy landscape for a metal surface to vacuum transition from a DFT calculation. The following pictures show a 2D slice of the potential, where potential energy is given ...
6
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0answers
79 views

Do exactly solvable stat mech systems admit efficient algorithms for finite sizes?

I come from a background in statistical mechanics (not algorithm design or complexity theory), and the following question occurred to me that I could use some expert help in beginning to understand. ...
6
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0answers
612 views

Comparison between Cadabra and other Symbolic Computer Algebra software [closed]

Does anyone has some experience about working with Cadabra and it's (dis)advantage in comparison to other Symbolic Computer Algebra software such as Maple and Mathematica (physics package) in the ...
5
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2answers
3k views

Quantum XOR: How do you generalize it?

Consider the classical XOR Gate: Given a 2 bit system: $G = [u_1, u_2]$ $$XOR(G) = (u_1 + u_2) \ mod \ 2$$ Is the following a good generalizaiton of a Quantum XOR Gate: Given a 2-qubit system: $...
5
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3answers
925 views

Good source for numerical simulations of Wigner function?

I'm interested in simulating the time evolution of a Wigner function for a harmonic oscillator (and possibly some other potentials) and I can't seem to find a good resource for that. My background in ...
5
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4answers
482 views

Supergravity calculation using computer algebra system in early days

I was having a look at the original paper on supergravity by Ferrara, Freedman and van Nieuwenhuizen available here. The abstract has an interesting line saying that Added note: This term has now ...
5
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1answer
4k views

How to measure the spin-spin correlation in a Monte Carlo simulation of the Ising model?

I'm simulating the Ising Model in 2D up to 5D and I want to calculate the spin-spin correlation, correlation length, and critical exponent of the system. What is a good way to go about doing this? ...
5
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1answer
1k views

How to calculate Zak phase from numerical wavefunctions with arbitray phase?

In numerical calculations, an arbitrary gauge or phase attached to a wavefunction at a particular $\mathbf{k}$ places an obstacle in calculating the Berry connection $$\mathcal{A}(\mathbf{k})=\langle ...
5
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1answer
156 views

Validity of finite difference method

I am using the Finite Difference Method to solve Poisson's equation $$\frac{\partial \phi}{\partial z^2} = \frac{\rho}{\epsilon}$$ To do it is discretized according to the Finite Difference ...
5
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1answer
86 views

Methods for handling close approaches in $N$-body simulations

In direct gravitational $N$-body simulations, what are the preferred methods for handling close approaches between bodies in order to preserve the accuracy of the evolution of the system?
5
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2answers
207 views

Is it possible to propagate a relativistic system of particles in time using Verlet?

The Verlet algorithm and its derivations are very popular methods to integrate Newton's equations of motion in time and obtain a trajectory for a system with $N$ particles. I work with classical ...
5
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2answers
2k views

Can I use imaginary time propagation for many-body problems?

There are various ways to numerically find the ground state energy and wavefunction of a many-body Hamiltonian. You can diagonalize the Hamiltonian and pick out the lowest eigenstate, or you use ...
5
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1answer
605 views

Calculating a two-dimensional orbital path with infinite granularity (non-Euler integration)

For a game I am making, I am trying to calculate the position of an orbiting object around one or more bodies. I have successfully implemented this gravity simulation by calculating the force, then ...
5
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1answer
143 views

Numerical relativity resources - Adaptive Mesh Refinement

I have, in the past few months, been studying numerical relativity, specifically the problem of spherical collapse of a scalar field as studied by Choptuik. I have also taken a look at some books that ...
5
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1answer
493 views

Machine learning and Condensed Matter Physics [closed]

What is the state of art of the use of Machine Learning algorithms in Condensed Matter Physics and Phase transitioning? Is there any promising result that lead us to think this is a good way to pursue?...
5
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1answer
251 views

Distribution of orbital velocities in a disk galaxy for N-body simulation?

I'd like to write an N-body simulation in which I collide two disk galaxies. To give you an idea of the accuracy I'm trying to achieve, I'm aiming to make this my screensaver at 30fps on my work ...
5
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3answers
1k views

Multiple colliding balls

I have written an algoritm to resolve a collision between two balls with conservation of momentum. It looks to work exactly as expected in my simulations. Here is the code: ...
5
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1answer
464 views

Least action principle — numerical simulation strangeness

I'm trying to get some experience with the least action principle, and for this I chose a simple 1-dimensional problem of a particle moving in some field. The least action principle would then look ...
5
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3answers
312 views

Simulate a physical impact of objects made of finite, small elements

I want to simulate an impact between two bodies according to gravity, and eventually considering other forces to stick matter together. I'd like to use python to do this, but I am open to alternatives....
5
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2answers
180 views

Numerical complexity of different quantum chemistry approaches

For the introductory course for the students I am trying to collect the brief overview of different quantum chemistry methods and their numerical complexity. The second point is surprisingly poorly ...
5
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2answers
215 views

What is the BG Equation?

About 45 years ago or so I was a Physics department staff computer programmer when I was a physics major undergrad. I worked with a professor doing research on nuclear shell models -- he was ...
5
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0answers
97 views

Do systems of fermions take longer to equilibrate than systems of bosons for complexity-theoretic reasons?

This excellent paper by Scott Aaronson persuasively argues that computational complexity can be relevant for physical processes. In particular, what's hard for a hypothetical Turing machine to do may ...
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0answers
595 views

Numerical Solution of the Propagation-Dispersion equation

I have asked this question on Computational Science and also on Mathoverflow, but no satisfactory answers so far. I thought maybe the physics community could shed some insight on the issue. I am ...
5
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2answers
206 views

Numerical Tools to find Braiding Statistics of Quasiparticles

While certain classes of systems that exhibit topological order can be solved exactly (such as the Toric Code, Abelian FQH Edges, etc.) there also exist systems (think of perturbed versions of the ...
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0answers
1k views

An explanation for the Landauer's principle

Has anyone understood the Landauer's principle? What is the current status? In specific, is there a theoretical derivation of the Landauer's Principle?(not the heuristic one based on Salizard's ...
5
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1answer
755 views

Ray tracing in General Relativity

I would like to find out what one would see at the Schwarzschild radius of a massive non-rotating black hole, if the black hole is surrounded by a bright ring. For that, I would place the observer at ...
4
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3answers
426 views

Future Computer Performance

Moore's law has succesfully predicted up to now that integrated circuit transister density doubles every two years. However, computer performance is dependent on additional factors like architecture, ...
4
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2answers
1k views

Rotation matrix of Euler's equations of rotation relative to inertial reference frame

I was playing with simulation of Euler's equations of rotation in MATLAB, $$ I_1\dot{\omega}_1 + (I_3 - I_2)\omega_2\omega_3 = M_1, $$ $$ I_2\dot{\omega}_2 + (I_1 - I_3)\omega_3\omega_1 = M_2, $$ $$...
4
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2answers
276 views

How does particle physics use deep neural networks to find particles?

Does anyone use deep learning: RNN, CNN or any other architecture of deep neural networks to asses the standard model or to detect new or unseen particles? What's the status these days in this ...
4
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1answer
489 views

Gravitational field of thin 2D ring - numerical simulation

I'm aware of Newton's Shell Theorem, which states that inside of a thin ring of uniform density, the gravitational force exerted on a point mass should be zero. I wrote a quick field simulation to ...
4
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3answers
455 views

Lexical/ontological/semantic knowledge base for physics

Are there lexical/semantic knowledge bases for physics that can be used for automated reasoning and AI (like Princeton's Wordnet and MIT's Conceptnet for common sense English usage)? If not in ...
4
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1answer
178 views

How to “build” a proton

Sabine Hossenfelder in her column The End of Theoretical Physics As We Know It made the following statement: For example, we have a perfectly fine theory that describes the elementary particles ...
4
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1answer
800 views

Euler Equations, Sod shock tube & conservation

Conservation of momentum? I am considering the Euler equations in conservative form and solving the Sod shock tube problem I have written a Godunov finite volume type solver. It solves for density ρ, ...
4
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2answers
308 views

What's the relationship between Density Functional Theory (DFT) and Kohn-Sham equations?

It seems Kohn-Sham equations are approximate methods to solve many body Schrodinger's equation. They directly split a multi-electron Schrodinger equation into many single-electron Schrodinger ...
4
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1answer
94 views

Can I re-wind gravity?

Suppose I perform an arbitrary simulation where I integrate the motions of a collection of particles which interact only gravitationally. Suppose I use a time reversible integrator (to be specific, ...
4
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2answers
901 views

Hamiltonian mechanics really useful for numerical integration? Lagrangian can become 1st-order

(I'm talking about the classical mechanics.) Many texts say that Euler-Lagrange equations are difficult to treat numerically because they are second-order ODEs, ${f_i(\boldsymbol{q, \dot{q}, \ddot{q}}...
4
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1answer
1k views

Industry application of computational quantum mechanics?

I was wondering if anybody knew of an industry application of computational quantum mechanics. For example, the efficient placement of circuit elements on a PCB is in part motivated by classical FDTD ...
4
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1answer
121 views

buiding circuits from color superconductors

caveat: the sort of exotic matter engineering in here is currently beyond the reach of our technology, but, that having been said: Has their been any research on building models of these sorts of ...
4
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2answers
126 views

Are the laws of physics bound by the same performance bounds algorithms are bound by?

Consider the problem of finding the convex hull for $n$ points on a plane. No constant time algorithms exist to solve it. Now say you represent the points as poles of equal height that you hammer ...
4
votes
1answer
289 views

Using the monte carlo method to compute the magnetic field of a curent carrying loop

I have written a program in cpp that computes the magnetic field at a point from a current carrying loop. It uses the biot savart law and the monte carlo technique to carry out the integral. The ...
4
votes
1answer
2k views

Some hints/introductions/textbooks for LBM (Lattice Boltzmann methods) fluid simulation?

I come from a computer science background and I want to learn details about LBM in fluid simulation. I have been searching around for a concise tutorial that tells me how LBM is used to solve a ...
4
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2answers
3k views

On numerically solving the Schrödinger equation

I just read a paper 'A pocket calculator determination of energy eigenvalues' by J Killingbeck (1979). Link: http://iopscience.iop.org/0305-4470/10/6/001 I have some questions about section 2. Why $...
4
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2answers
319 views

Mass connected to spring on a frictionless surface vibrating out of control

I am not good at Physics so please bear with me. I am trying to understand harmonics and in order to do that I thought its best to ensure my understanding of the equations of motion is correct. To do ...
4
votes
1answer
1k views

Integral of Sedov's self-similar solution to the spherical blast wave problem

I'm studying the Taylor-Sedov self-similar solution to the problem of a strong explosion in a homogenoeus atmosphere. The problem is discussed in Landau & Lifschitz VI (in the 2nd edition it's §...
4
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2answers
678 views

Can the quantum eraser experiment result indicate a 'computed universe'?

The quantum eraser experiment tells us that a photon shot at two slits is a wave, unless you measure which slit is taken and you do not destroy the measurement result. I've found this very similar to ...
4
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2answers
216 views

Faster ways of computing feynman diagrams

Obviously the machinery of QFT allows us to calculate processes, such as QED diagrams, to great precision, and whilst it is effective, it seems there are many processes that make calculations (say by ...