Questions tagged [computational-physics]

Computational physics is the study and implementation of numerical algorithms to solve problems in physics for which a quantitative theory already exists.

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308 views

1-D turbulent energy spectra in homogeneous direction (non-isotropic)

I am trying to compute the one-dimensional energy spectra for my channel-flow simulation. I have already written a post-processing script to achieve this; however, I need to validate my code before ...
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0answers
53 views

Parallelizing molecular simulation with full configuration energy

First, let just me stress that I'm not a an expert in computation chemistry, so now the problem: We have GCMC molecular simulation, in the Grand Canonical ensemble, using the standard metropolis ...
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1answer
109 views

triple cross prouct of tensor

Im trying to compute a triple cross product of vectors a,b, and c in real space and integrate over the entire space. The result is a term in the hamiltonian for an electronic system so there are ...
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0answers
227 views

Physics of explosions: just vorticity?

eg 1 2. Is it just vorticity? What's actually happening? (Similar: steam engines, volcanoes, clouds). examples are grid-based, using "vorticity confinement" in Phoenix FD. EDIT Some techniques: "...
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43 views

Software suggestion for simulating the stacking of sedimenting rods

I'd like to simulate the following problem: Define some square, horizontal and hard area onto which cylinders (aspect ratio R) sediment. Preferably, the source of cylinders sequentially generates N ...
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177 views

Mass conservation in atmospheric continuity equation numerical solution

My phd project is heavily related to numerical modeling of planetary atmospheres. In particular now I am dealing with a particular expression of the continuity equation, involving a thermodynamic flux....
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0answers
64 views

Sensitivity Analysis — Total Variation for a function with categorical arguments?

I have an application in sensitivity analysis of complex system models with moderately nonlinear interactions between arguments Arguments potentially dozens or hundreds in number Arguments mostly ...
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0answers
95 views

The Schrodinger equation for time-dependent Hamiltonian after one timestep, taking exponential or use ode solver?

The Schrodinger equation for time-dependent Hamiltonian is $$i\hbar\frac{d}{dt}\psi(t) = H(t)\psi(t) \, .$$ Assuming I knew $\psi(t)$, I want to know $\psi(t+\Delta t)$. Should I take exponential ...
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0answers
74 views

Metropolis algorithm and thermal sine-Gordon model

I try to simulate thermal version of 1D $(x, t)$ sine-Gordon field model. I am interested in finding thermal static solution that minimizes functional of energy $E$: $$E = \int dx \left( \frac{1}{2} \...
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101 views

How to get the eigenvalues of Hamiltonian in an over complete basis

Let $|\psi_i\rangle$, $i=1...N+m$, be a set of overcomplete basis vector in a $N$-dim Hilbert space. The following are known: (Einstein's summation convention assumed) $$\hat{H}|\psi_i\rangle=H_{ji}|\...
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49 views

Book Recommondation for the time-dependent Schrödinger equation [duplicate]

Can you recommend a good book that discusses several methods for the numerical solution of time-dependent and time-independent Schrödinger equation? I have searched the internet several times but ...
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64 views

RCWA for Non-Periodic Structure?

I have a quick question regarding Rigorous Coupled Wave Analysis (RCWA) for numerically solving problems (in optics). I am trying to simulate a device which is non-periodic in x, y directions (but is ...
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84 views

Representing a 3D system in 2D (Electromagnetic modelling)

Ok so I'm a complete beginner in computational modelling (I use analytical methods of physics typically) but I would like to model an anisotropic, aperiodic (but not random) finite array of metallic ...
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1answer
463 views

Shooting method - Matlab ODE

I'm trying to solve these equations of hypersonic adiabatic flow over a flat plate. I did all the simplifications and got these equations for the stagnation point flow. $$\left(Cf''\right)' + f f'' = \...
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467 views

Is this the correct way to calculate the Madelung constant?

I'm trying to compute the Madelung constant of the ZnS lattice. The method is as follows: The lattice is a face-centered-cubic with basis $S^-: (0,0,0)$ and $Zn^+: (1/4,1/4,1/4)$. The Madelung ...
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86 views

Time dependent self-consistent equations

I am facing the following problem. I need to solve numerically a set of coupled equations $$i\frac{d}{dt}f_{n}^{(i)}(t) = \left[U\cdot n(n-1) + \mu\cdot n\right]f_{n}^{(i)}(t) - \sqrt{n+1}\Phi_i^{*}\...
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811 views

BiCopter simulation in Matlab

I derived a bicopter dynamical model with two servos and two BLDC motors. And now am trying to simulate it using Matlab. As base for simulation I used this paper and this code Unfortunately, the ...
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74 views

fixed point iteration to find out second order non-linear diff equations

I am working on some model analysis, getting two diff equations and after I convert them into matrix form, I have equations looks like $$ [A][X]=C\times\big(\exp([B][X])-1\big), $$ where $C$ is a ...
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104 views

Conservation at grid interface in adaptive mesh refinement

I am using adaptive mesh refinement to solve one dimensional inviscid Burgers equation. However I am facing some difficulty to handle grid interfaces which are not uniform (coarse-fine grid interface)....
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0answers
618 views

radially averaged power spectrum of a binary image does not look like power law

It has been known that Fourier power spectrum somehow obeys power law therefore the slope of the spectrum can be used to calculate the fractal dimension of an image. Many people have used it for ...
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294 views

Spin-spin correlation functions in the Ising Model Monte Carlo [closed]

I'm using the Metropolis algorithm for 2D up to 5D for the Ising Model and I want to compute the spin-spin correlation function. $$c(r)=<s_is_r>−〈s_i〉〈s_r 〉$$ but I'm not sure how to estimate $...
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640 views

Can you provide me with the source code of DMRG writen by C++?

I want to study the Density matrix renormalization Group(DMRG). Can some one provide me with the souce code which is writen by C++ for study purpose only? The code is not necessiary very professional, ...
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0answers
299 views

Two Dimensional Nozzle Flow

I've been looking at the book "Computational Fluid Dynamics - The Basics With Applications", by John D. Anderson, and his solution for the one-dimensional subsonic-supersonic nozzle flow using the ...
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0answers
45 views

Understanding the use of Minimum Translation Vector (MTV) for an elastic collision response

So, I'm trying to simulate polygon rigid body physics, both linear and angular. To calculate the MTV is easy in SAT (Minimum Translation Vector), and to use it to adjust position is also easy: ...
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0answers
35 views

Keplerian Orbit Estimator [closed]

While calculating the eccentric anomaly of a satellite using the Newton-Raphson method, what initial estimate of the root for E (eccentric anomaly) should be taken for least number of iterations(best ...
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3answers
310 views

Why there are people that still prefer fortran 77 over new versions?

I am reading some notes from a course in numerical analysis for physical sciences and it is my impression that there are still people that prefer Fortran 77 over new version due to the implicit ...
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2answers
380 views

Time step relationship with number of elements or material properties

When looking at the output file of my solver, I have been told that the time-step taken by the solver depends on parameters like the total number of elements and their relative size in my geometry, or ...
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1answer
238 views

How can an engineering student become a computational scinece expert in a short time [closed]

How can a student with zero computing or programming language knowledge, few engineering mathematics knowledge, understand computational science especially Finite Element Modelling (FEM) from ...
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1answer
203 views

Euler-Bernoulli beam element versus continuum beam element

I am using OpenSees to model a simply supported beam with a point load in the middle. The model is in consistent units. The beam is made up of bilinear quad elements. I have used 30 elements along the ...
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2answers
129 views

Validating conservation laws from physics

Say I'd like to implement a numerical model of a physical system (e.g. a simple wave equation). Of course the energy conservation law is valid for this system. Is there a way to validate that my ...
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3answers
242 views

What type of computer science/engineering knowledge someone need to have to study graduate level course in compurational physics?

I am wondering if this is the right place to ask this question. I found a related question on stack overflow https://stackoverflow.com/questions/814312/physics-in-computer-science but it was closed. ...
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3answers
857 views

Simple Simulation Examples in Computational Fluid Dynamics

I would like to incorporate a CFD topic in a project I currently have. The deadline is a little less than a month from now. Basically, what I would like to do is solve some equations and simulate ...
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2answers
167 views

General question about Computational Science

I'm student of computer science (BS) and considering computational science as the field to major in for MS program. I have two questions which might look silly but I'm really confused: 1- Are ...
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1answer
54 views

How to do Weierstrass-transform in MATLAB?

I have a diagonalization problem. I have the eigenstates correctly, and I want to do a Gaussian-smearing (Weierstrass-transform) on them. So I have the wave functions ($\Psi$), and the continuous ...
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2answers
87 views

Overrelaxation with w < 0

Are there any circumstances under which using a value $w < 0$ would help us find a solution in over-relaxation faster than we can with the ordinary relaxation method? Over Relaxation Method: $$x'=...
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1answer
100 views

coupled equations with finite difference method

I have these three differential equations in which I need to solve numerically: $$ \frac{dn_0}{dt}= -n_0(t)W_{01}(t) + n_1(t)K_{10} $$ $$ \frac{dn_1}{dt}= -n_1(t)W_{12}(t) - n_1(t)K_{10} + n_2(t)K_{...
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1answer
265 views

Poincare map for Arnold-Beltrami-Childress Magnetic Field in Python

I want to plot the Poincare map for Arnold-Beltrami-Childress magnetic field for parameters $A=1, B=0.816, C=0.5773$ in Python for the Poincare section $z=0$. Also, I am not able to understand what ...
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1answer
67 views

Conservatives in shock tube

We know shock tube problem will give discontinuous solution of primitive variables ($\rho$, $v$, $p$). Will it give discontinuous result in flux terms? $F =[\rho u, \rho u^2 +p, \rho e_v]^T$. I tried ...
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2answers
344 views

What multibody dynamics softwares exist?

I have used the free, multibody dynamics software MBDyn for a while now. It is a good program and also fits my needs. There are good manuals, basic tutorials and examples to be found. There is also a ...
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1answer
88 views

Indexing Nested Loops in C [closed]

I am having trouble indexing correctly the below statement in C inside a function and then returning it as a pointer. The returning part should not be confusing - hopefully - however the indexing is a ...
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1answer
498 views

The condition for stability using the leapfrog method

I have the ODE below $$\frac{d}{dt}\pmatrix{x\\ y} = \pmatrix{0 &1\\-a &0}\pmatrix{x\\ y} \enspace .$$ The $m=1$ leapfrog method is defined as: $$y_{n+1} = y_{n-1} + 2f_nh \enspace .$$ For ...
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1answer
105 views

How many sample points are needed when re-constructing linear combination of 2D polynomials defined over unit circle?

I have a set of first 25 Zernike polynomials. Below are shown few in Cartesin co-ordinate system. z2 = 2*x z3 = 2*y z4 = sqrt(3)*(2*x^2+2*y^2-1) : : ...
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1answer
69 views

Unexpected behavior, values tend to converge instead of fluctuate. (MD)

I am writing a molecular dynamics program to create an lattice and populate it with atoms/molecules. These then are given random velocities and the system is initialized. Then throughout time the ...
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1answer
146 views

MAX-SAT and MAX-cut

I have been using MAX-SAT solver to obtain the exact ground state of ising spin glass model: For 1D periodic model, for systems with 50 binary variables and interaction range of 15th nearest ...
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1answer
68 views

Particle Collision to Static paticles

I have a system of particles with equal distance with each other and another at random positions which is moving with time. I want to know: a) The method by which I can reduce the number of particles ...
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1answer
79 views

Computer build for scientific or big data computing [closed]

I'm wanting to build a computer for scientific or big data computing (Python, Fortran, Matlab) and I was hoping to get some advice on the type of processor, memory, graphics, etc I would need. I ...
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1answer
31 views

How to implement the Impulse Based Dynamics for the rigid body dynamics simulation?

I am having hard time learning the method of impulse based dynamics developed by Mirtich for rigid body dynamics simulation. Please help me out if any body has any example code(algorithm) of it. ...
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1answer
75 views

Stability of PDEs

I am currently trying to solve some PDEs with FiPy. At page 56, the manual mentions (https://www.ctcms.nist.gov/fipy/download/fipy-3.0.pdf). The largest stable timestep that can be taken for this ...
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1answer
65 views

ISING2D with Mathematica. Searching a correct way to compute the heat capacity (mean values over several iterations)

I'm trying compute the heat capacity $C_v$ out of my simulation for the 2D-Ising model which is given by $C_v = \frac{\langle E^2 \rangle - \langle E \rangle^2}{T^2N^2}$ ($E$: Energy, $T$: ...
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2answers
65 views

How to calculate $g_r$ when using the cell method algorithm

I have a self-written MD code in C++. I am simulating atoms using the Langevin dynamics model. I use the linked-cell method to speed up the simulation; as a result, atomic interactions are only ...