Subdiscipline of theoretical physics which consists in the study of physics problems using numerical algorithms. PLEASE NOTE that questions about computational methods and/or programming are OFF-TOPIC on Physics.SE.

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Monte Carlo Metropolis method - trial step algorithm [migrated]

I'm working on a Magnetization simulation and writing an algorithm using the metropolis method. I am using a change in energy and a Boltzmann distribution, but, my question is about the trial step. ...
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2answers
55 views

time step in kinetic montecarlo simulation

I have a doubt about how the time step is calculated in kinetic montecarlo simulations. One state with index $i$ is connected to other $N$ states, indexed by $j=1...N$, by transitions that happen ...
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11 views

Explicit solvent simulations in NVE ensemble: Molecular Dynamics

I am simulating a SDS micelle system in NVE ensemble at room temperature. I am not sure if the system is equilibrated, since the pressure variations are around 100's of atm, where the average pressure ...
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0answers
14 views

Efficient ways to solve complicated kinematics problems

I'm curious about the range of approaches one can take to perform motion/kinematic simulations on many 3D objects. Currently I am familiar with the iterative process of doing such a simulation, that ...
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20 views

Books on Spectral Jacobian

Can anyone point me a book to better understand "spectral Jacobian". I am studying X-parameters, I have the book X-Parameters: Characterization, Modeling, and Design of Nonlinear RF and Microwave ...
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11 views

Initial guess for calculating the Universal Variable Formulation of the two-body Kepler problem

I am trying to simulate orbits using the Universal Variable Formulation of Keplers two-body problem, using the algorithm provided by Howard curtis in Orbital Mecanichs for Engineering Students as per ...
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26 views

Open-source code for computing response functions

Summing Feynman diagrams to compute the response functions of a microscopic model is common in many areas of physics. While conceptually straightforward, the task can be computationally intensive. ...
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20 views

Monte Carlo simulation of Breit-Wigner

I am using a Monte Carlo approach to integrate a scattering amplitude which has a propagator-squared term like $f(s)=\frac{1}{(s - 4)^2 + 1}$, between $s=0$ and $s=20$. Using a uniform random ...
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2answers
119 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = ...
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1answer
69 views

Tight binding Hamiltonian for 2D finite dimensional lattice and nanowire

The Hamiltonian of a 1D lattice having finite N atoms, (if we consider one basis per atom) is given by the following N by N matrix- Here 'E' is the onsite energy and 't' is the hopping integral. ...
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1answer
77 views

Numerically solving a simple Schrodinger equation with fast Fourier transforms

While trying to solve a stochastic Gross-Piaevskii equation I have found a problem that can be tracked down to something buggy occurring in the simplest Schrodinger equation possible: $$\partial_t ...
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38 views

Electromagnetic scattering $T$-matrix in MATLAB

My problem with the inverse of the matrix T (in the photo) , the matrix consists of Bessel and Henkel functions in high order (the orders from 1 to 21), then the elements of this matrix arrived to ...
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1answer
47 views

Quantification of uncertainty, or information loss, when modeling a physical system?

Say I have a physical circuit (say a battery, wires and an incandescent lamp) that I want to model. To model it I could perhaps use: traditional circuit theory some kind of finite element analysis ...
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2answers
85 views

Statistical specific heat as energy fluctuation in spin glasses

Consider the specific heat (in statistical sense, as energy fluctuation in the canonical ensemble) of a complex model, something similar to a spin glass. Is the specific heat defined on fluctuations ...
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0answers
44 views

About multi dimensional numerical integration [closed]

I want to calculate 4 dimensional phase space integration.If anybody help me with a general 4 dimensional integration that will be OK. I can apply trapezoidal or Simpson's rule in lower dimensional ...
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0answers
36 views

Model of the solar system orbital periods [closed]

I've written a program to model the solar system. I am now testing its accuracy. I've checked conservation of angular momentum, and it is perfectly conserved. I've also plotted the path of the ...
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5answers
1k views

Why do objects in a gravity simulation experience sudden large accelerations?

I'm trying to create a simple program that simulates gravity. The idea is that I have one central sun and several planets that I can create with a swipe gesture on the screen, and I use the initial ...
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1answer
26 views

Testing the accuracy of a solar system simulation

I've written a java program to model the solar system, and I need to test its accuracy. What would be some good ways to do that? I've checked for conservation of energy and angular momentum. I'm using ...
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1answer
30 views

Lollipop 3d choreography animation

I initially wanted to recreate the little dancing dots android lollipop's boot animation in javascript: For that, I've implemented a 3d $n$-body simulation (with css and js): ...
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0answers
20 views

Package for flavour physics computation? [closed]

Which softwares one usually uses for flavour physics related calculations? I saw one called SUSY_FLAVOR. I haven't used it yet though. What in case of other BSM models other than SUSY? Is there any ...
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0answers
45 views

Software engineer vs physics engineer vs computational physics [closed]

Don't know if this question is off topic, but i think it is the best place to get an answer. I am finishing the 3rd year of a degree in physics engineering. I enjoyed the first year, but in the ...
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2answers
219 views

Why do we still use perturbation theory, when we have advanced numerical methods and fast computers?

If my question sounds ignorant or even insulting, I apologise. I may be completely wrong, since I'm not a theoretical physicist. So, I understand why perturbation theory was originally used in ...
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0answers
45 views

Numerical problem with Hartree-Fock equations for dilute Bose gas

I have to solve the following set of equations self-consistently: $$\begin{align} n_c(\mathbf{r}) & = \frac{1}{g}\left[\mu - V_{\rm ext}(\mathbf{r}) - 2 g n_{T}(\mathbf{r}) \right] \\[3mm] ...
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2answers
71 views

Can lens designs be brute-force computed to create optically precise equipment? [closed]

It seems lens design hasn't changed much over the last 50 years or so with many older manual lenses still very much being used today. Can the order, distance between and type of lens elements be brute ...
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1answer
22 views

How to choose basis functions that contribute most efficiently per term? [closed]

I would like to approximate some positive, scalar function $f(x,y) > 0$ on a 2D field of finite size i.e. $x\in [a,b],y\in[c,d]$ I am familiar with the set of basis functions used in the Fourier ...
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1answer
46 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 ...
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1answer
52 views

Conversion of satellite coordinates from ITRF to J2000

I have coordinates of various satellites in two coordinate systems: Cartesian coordinates in the international terrestrial reference frame (ITRF) RA / DEC in J2000 epoch, as derived from plate ...
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54 views

What is an intensive property of a fluid?

Let's assume we are considering a fluid which occupies the bounded domain $\Omega_t\subseteq\mathbb R^d$ at time $t\ge 0$. Let $c\in\Omega_0$ be a particle of the fluid and $$x_c:[0,\infty)\to\mathbb ...
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1answer
27 views

Does *advection* describe the change of density of massless infinitesimal tiny *thingies* injected into a fluid?

I'm considering an incompressible Newtonian fluid with uniform density and try to figure out what's meant by the term advection. Let $\Omega_0\subseteq\mathbb R^d$ be an (infinitesimal small) bounded ...
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0answers
37 views

How to calculate dispersion relation from a Finite Difference (FD) wave simulation

I have a python code that calculates the solution of the inhomogeneous acoustic wave equation for a 2D medium with any velocity and source configuration. It was implemented using Finite Differences ...
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1answer
61 views

What is the time imaginary method? [closed]

I have to submit homework about the scheme which solves the time-independent Schrödinger equation and finds the ground state by the imaginary time method. I know the substitution ...
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0answers
27 views

Numerically evaluating momentum sums

For many-body systems, calculations often involve momentum sums, which are ultimately evaluated numerically for a finite system size $N$. The larger $N$ is, the more accurate the results. Is there ...
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1answer
21 views

Numerical computation of electric multipoles

I'm trying to do a plot of the first multipole terms in Mathematica. My plot isn't what I expected, so maybe my problem is in the mathematics. Following the Griffiths' book on Electrodynamics, the ...
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67 views

Experiments to resolve dillema between continuity and discrete

Which experiments/experimental methods are suggested to resolve an alternative about the structure of our universe space and time - is it continuous or is it discrete in a very small scale, especially ...
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1answer
68 views

Numerical relativity in causally pathological spacetimes

To perform numerical relativity simulations one almost universally adopts the so called "3+1" approach: spacetime is divided up into spacelike slices, each representing a "moment in time". After some ...
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27 views

canonical ensemble density matrix numerical integration of the von Neumann equation

I am working with a numerically calculated Eigensystem of a given non-linear Hamiltonian. As a test I integrated Schrödinger equation for each eigenstate in time with Dormand Prince 54 and also Runge ...
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6answers
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Is there any aspect of an explosion resulting from a nuclear weapon test that cannot be simulated using super computers?

This Washington Post news article states that with the advent of computer simulation of nuclear tests, live tests are no longer needed. Generally speaking there are 3 aspects of an explosion ...
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1answer
39 views

Single fluid simulation algorithm

Every fluid simulation I've seen implicitly involves a fluid that isn't mentioned, usually air. This is clear because the simulation usually has an ambient temperature, and always an ambient velocity. ...
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1answer
27 views

Why will a Fourier transform of a pickup placed at the middle of a string only result in odd harmonics?

My physics teacher explained a lot of information about strings but he never went in depth with my question. What happens to the even harmonics and why are the odd ones the only ones picked up?
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33 views

recovering numerical wave function using path integral after Wick rotation

I have written two different path-integral codes, PATHINT and PATHTREE, to numerically solve some classical-physics problems in nonlinear systems, finance and neuroscience. They work just fine. My ...
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2answers
168 views

Do electrons actually reside in orbitals?

(Following this answer on Chemistry.SE) Let's define "dwell"/"reside" as the area in which the probability to find an electron is more than 90%, for example. Calculated orbitals comprise a basis ...
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18 views

Heat transfer in liquid helium channel connected to “infinite” reservoir

I am trying to solve the temperature distribution in liquid helium using numerical analysis (OpenFOAM for those who are familiar with it). One part of the fluid is contained in a narrow channel, one ...
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0answers
64 views

Graduate level orbital mechanics book

I recently finished an undergraduate course in classical mechanics and really enjoyed the subject, particularly the sections regarding the mechanics of orbits. I am considering pursuing a graduate ...
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1answer
44 views

Difference between finite volume, characteristic method and plug flow models of a pipe

I have to model pipes (of a district heating network) with ODE's. My background is computer-science, so it is not that easy for me to understand different approaches. Finite volume approach. Method ...
2
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0answers
35 views

Is the finite element method easily extrapolable to new disciplines? [closed]

I am a structural engineer with a good solid mechanics background. I am reasonably familiar with finite element methods as applied to linear/nonlinear solids and structures, I would like to know how ...
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0answers
35 views

Comparing two versions of the same hydrodynamic code and their error

So I have two versions of a hydrodynamic code that has the same underlying physics. Lets call them code A and B. However code B is more optimized and more object oriented. I was trying to compare the ...
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0answers
92 views

How do you fourier transform a tight binding hamiltonian numerically?

The task is to do a fourier transformation of a tight binding hamiltonian of a 1D-chain with unit cell size 2, but even after many tries and googling I still don't have a idea how to do it correctly. ...
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2answers
59 views

Obtaining Velocity from Acceleration

I'm following a research paper (PDF via RG), part of which is about using the accelerometer of a smartphone to assist the user's positioning via WLAN. Accelerometer is used to determine if the user ...
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2answers
87 views

Exact Diagonalization of a BdG Hamiltonian on a Finite Lattice

I would like to numerically find the edge modes of a $p_x$ + $i p_y$ BdG Hamiltonian. The lattice version is given by H = $\sum\left[-t \left(c_{m+1,n}^{\dagger} c_{m,n} + \text{h.c} \right) - ...
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Numeric fermiomic creation operators and unit cell

I have to do some numerics (e.g. FFT in Maple/Octave) on a 1D fermionic chain without forces between the particles. The description says that two sites build an unit cell. What does this mean? And ...