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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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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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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111 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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646 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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0answers
302 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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673 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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303 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
54 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
521 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
549 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
109 views

Why the magnetisation shows abrupt behaviour for this 3D ising spin system

I am trying to simulate a 3D Ising spin system (+1 & -1) using Monte Carlo Metropolis Algorithm. I want to get different physical quantities from this simulation like magnetization, Average Energy,...
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1answer
247 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
279 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
132 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
258 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
919 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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1answer
93 views

Applying weak form

I have two dimensional equation and I want to solve it using Finite Element Methods. $$ \nabla . (\alpha(x,y)\nabla u(x,y)) + \dfrac{\partial u(x,y)}{\partial x}+\dfrac{\partial u(x,y)}{\partial y}+u(...
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1answer
140 views

Scattering of waves in a symmetrical potential (using python)

I'm looking at scattering of waves in a symmetrical potential as part of a research project. If a plane wave $e^{(ikr)}$ is incident on a spherically symmetric potential $V(r)$ the scattered wave is ...
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2answers
175 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
66 views

Acoustic Simulation, how are boundaries handled?

I don't have a background in numerical modeling so this question is rather broad. What I am interested in is modeling the propagation of an ultrasonic acoustic wave in 3d space. The basic 3d wave ...
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1answer
133 views

Conserve energy by message passing?

There are $N$ particles with positions $x_i(t)$ and velocities $v_i(t)$ and mass 1. There is a potential function $U_{i,j}(x_i, x_j)$ between each pair of particles, which is $0$ unless the particles ...
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1answer
39 views

MATLAB ode45 doesn't start at initial conditions

I wrote a code in MATLAB to solve a system of differential equations, but my solution doesn't seem to take into consideration the initial conditions I specified. I am not sure how to interpret this ...
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2answers
106 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
158 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
466 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
71 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
416 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
89 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
111 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
70 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
158 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
69 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
43 views

Error too large in leapfrog method for solving the wave equation of a vibrating string

I have been trying to figure out what I did wrong for the last two days. I do not know if I actually did something wrong or if the error is supposed to be this large in usual leapfrog problems. I ...
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1answer
61 views

Sum of random variables - Check your derived distribution against a numerical calculation/histogram

Consider independent random variates $X_0, X_1, . . .$ each uniformly distributed on the support $[0, 1)$ Let's say $Y = X_0 + X_1$, where $X_0$ and $X_1$ are independent uniform random variables with ...
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1answer
66 views

Getting streamline for a lid driven cavity flow in openFoam/ParaView

I have installed openFoam on Debian GNU/Linux and learning from official user guide. I have a problem with generating streamlines. I am trying to generate streamlines as explained in the post ...
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1answer
66 views

Smoothed Particle Hydrodynamics: Weird clustering of particles. Is that normal?

I implemented a rather simple SPH simulation using a cubic-spline-kernel and a simple non-iterative pressure solver as described in this PDF in equation 9. I followed algorithm 1 of that paper (...
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1answer
86 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
35 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
84 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
76 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
77 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 ...
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1answer
923 views

Boole's Rule in python

This is my first post in this forum so please forgive me if it is not the way it should be. My problem is about implementing "Boole's rule" into python. I have succesfully implementet trapezoidal and ...
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1answer
79 views

Help understanding this numerical surface integration technique?

I'm attempting to write a FORTRAN program that calculates the magnetic field, B, at any point outside of a bar magnet. I'm going to use a first order euler scheme, where each side of the bar magnet ...
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1answer
69 views

Converting acceleration over time to velocity or speed in code

I have acceleration data from a sensor. X Y & Z. I move the senor in the Y axis. Mostly in a straight line. So I ignore x & z. From the sensor documentation 5.2.1 Acceleration output: ax=((...
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2answers
70 views

Physical meaning behind the choice of the proposal distribution in Markov Chain Monte Carlo (MCMC) methods

Let us consider the conventions on names used in the theoretical derivation of Metropolis-Hastings Monte Carlo as outlined here, for the sake of common nomenclature. What we are building is a step-...
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1answer
2k views

Solving Time dependent Schrodinger equation using MATLAB ode45 [closed]

The Schrodinger equation for time-dependent Hamiltonian is $$i\hbar\frac{d}{dt}\psi(t) = H(t)\psi(t) \, .$$ I try to implement solve the Schrodinger equation for time-dependent Hamiltonian in ODE ...
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1answer
81 views

Mechanics - Rotational Inertia

I am facing a problem solving a mechanical system which is shown in the scheme below. We assume that coupling of the two shafts is done with a clutch Equations: $$J1*\frac{d\omega1}{dt} + Td(\...
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1answer
133 views

Solving differential equations in MAPLE (ballistic curve problem) [closed]

TASK: Make a simple animation of an object shot from a catapult. Object is moving through a medium. The problem must be solved in MAPLE. NARROWING OF THE PROBLEM: 2D problem consider atmospheric ...
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2answers
3k views

Most efficient library to diagonalize exactly large hermitian or unitary matrices

I am working on a physics problem which requires obtaining the exact eigenvalues and eigenvectors of Hermitian and Unitary matrices numerically. Naturally I would like to ask the experts what are the ...

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