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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Efficient weak form for numerically generating a static magnetic field from arbitrary current distribution (FEM)

This may stray into computational physics, but I'm curious to know if there is some more efficient way for what I am trying to do. Perhaps a better gauge formulation is needed. Consider two ...
-1
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0answers
26 views

SU(2) Coherent State and Probabilities

The SU(2) Corherent State for a for more than 1 two level system is given by: $$ | \eta, J \rangle = (1 + |\eta|^2)^{-J} \sum_{m=-J}^{J} \sqrt{\binom{2J}{J + m}} \times \eta^{J + m} |J, m \rangle, ...
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1answer
179 views

Potential function - numerical simulation

Using MATLAB, I fixed the potential in a region inside a rectangular plate (100 V) and in the border (50 V). I got the following result of the potential along the plate: I can't find an intuitive ...
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0answers
25 views

Book on galaxy formation and theoretical astrophysics for physics graduate [on hold]

I am looking for a graduate level book on galaxy formation and theoretical astrophysics and also numerical relativity for a graduate student who has completed quantum field theory and general ...
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0answers
12 views

Capturing superfluid condensation with exact diagonalization

Doing exact diagonalization on bosonic systems is tricky, because the possibility of multiple occupancy means that even the single-site Hilbert space is infinite-dimensional. It's my understanding ...
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20 views

What should I study if I am interested in creating innovative gadgets? [on hold]

I’m interested in gadgets and I know it requires programming skills. But on the other hand I really like experimental physics. So, I don’t know how to combine these science areas together.
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10 views

Newton's law - satellite position (in 2D) for specific moment of time [on hold]

I’m trying designate function that calculate satellite position (2 dimensional) for specific moment of time for better understanding Newton's law of gravity. To verify my calculations I created second ...
-2
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24 views

Imaginary part in calculation [on hold]

I want to simulate (I use mathematica) a matrix that has imaginary number. Given the matrix, $$A = \begin{pmatrix} e^{2I+3}Sin{(2\Pi t)} & e^{I (\Pi)}Cos{(2\Pi t)} \\ Cos{(2\Pi t)} & -e^{...
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49 views

Please explain this project to me [closed]

I've been struggling with this project for a few months now and I frankly can't break out of my way of thinking. The questions I'm struggling with understanding are written down below. The questions ...
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0answers
27 views

Total eigenvalues [closed]

I have a program as shown below: ...
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1answer
42 views

Meaning of $\nabla_{\mathbf{p}_k} W(\mathbf p, h)$ in PBF

I'm reading this paper on Position Based Fluids and I couldn't understand the meaning of $\nabla_{\mathbf{p}_k} W(\mathbf{ p_i - p_j}, h)$ in the equation 7 (see below). …the gradient of the ...
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0answers
20 views

Young's modulus graphene nanoribbons [closed]

How to calculate volume and young's modulus in graphene nanoribbons? How to calculate second derivative Total energy on the strain? Band structure of graphene nano-ribbons is the code below: ...
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4answers
326 views

Why don't hexapods gallop?

I haven't observed any terrestrial hexapods that gallop like agile tetrapods(cheetahs/horses). Instead, I've observed that all of them scuttle which constrains their maximum velocity. And after ...
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1answer
43 views

Heat transfer in solidification of cylindrical billet

I am trying to plot IN MATLAB the temperature profile of solidification of metal in manufacture of cylindrical billets. The metal is solidifying and the billet moves downwards as a constant water ...
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0answers
80 views
+50

Computational scaling of quantum and classical Monte Carlo algorithms

How does the computational complexity of finding an equilibrium thermal state for a given Hamiltonian at a given temperature scale with system size under classical and quantum Monte Carlo? I know ...
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2answers
563 views

System that is more efficient to simulate than to compute

I know some physics calculations require alot of computing to solve. Are there currently systems where it is more logical to do an experiment to "let the universe simulate the experiment for us" and ...
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0answers
35 views
+50

Calculating 2 particle Partial Trace for Density Matrix in Zeeman basis for a large number of Spins

I want to trace out all spins but 2 from a density matrix in the zeeman basis for N spins. For N=3 for example I would have the basisvectors: $ |S=1.5, m=-1.5\rangle =|000\rangle, |S=1.5, m=1.5\rangle ...
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1answer
51 views

Is Schmidt Decomposition well defined for periodic matrix product representation(MPS)?

We are able to perform Schmidt decomposition for open-boundary MPSs with dimension of boundary bond $m_0 = 1$, $|\psi\rangle=\sum w_{a_l}|a_l\rangle_L|a_l\rangle_R$. Because we can make $|a_l\rangle_{...
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69 views

How to plot numerically the wave functions according to the Hamiltonian?

It is often difficult to analytically solve the Schrodinger equation, and so we need to obtain a solution numerically. An example plot is shown below. Here, the wave functions for a three junction ...
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0answers
41 views

What is the best order of learning mathematics before start Monte Carlo Methods for Physics simulation? [closed]

I doing medical physics masters and hope to start my research in Monte Carlo methods to simulate some particle interaction and hence to calculate some unknown physical quantities ( Stopping power and ...
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0answers
34 views

Mathematica code for self-consistent field loop in Hartree-Fock method

I want to write a Mathematica code for Hartree-Fock treatment of helium (or hydrogen molecule-> namely two electrons systems) , but I don't know how to write a loop for self consistent field procedure....
2
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0answers
52 views

Efficient Method for Multiplying Angular Momentum Operators

I'm doing a calculation that involves canonical symmetrization of angular momentum. For example: $H_{\text{classical}} = J_x J_y \rightarrow \hat{H}_{\text{quantum}} = \frac{1}{2}(\hat{J_x}\cdot \...
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1answer
61 views

Finding $\pm 2 \pi$ defects in 2-D lattice nematic simulation

I'm working on a Monte Carlo simulation of a two-dimensional nematic system (XY-like model with even-order Legendre polynomial interactions, such that the director angle $\theta$ obeys $\theta \equiv \...
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0answers
14 views

Modelling a flow due to an oscillating hemisphere?

Say I have a long cylinder filled with air, closed at one end and open at the other. Now say I place a compressible hemisphere at the closed end and make it oscillate (compression and expansion of the ...
3
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0answers
57 views

Simulation of plasma in tokamak

I am reading some papers on numerical algorithms for simulation of plasma in the context of nuclear fusion in a tokamak. I am getting a little lost as there is a huge number of references, and it is ...
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1answer
46 views

Lattice QFT: Non-homogenous lattice spacing

I am interested why we fix the lattice spacing, $a$ to be homogenous in all dimensions. After a Wick rotation, $a=i \epsilon$ where $\epsilon=t_{i+1} - t_{i}$ and with euclidean time given by $\tau = ...
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38 views

C libraries for Solid State Physics

During last year I've attended courses of solid state physics, and I studied methods for bands structure calculations in the Hartree Fock framework. However, I know only theoretical aspects of these ...
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0answers
38 views

“Instantaneous” time stepping with time dependent Hamiltonian Schrodinger equation

The Schrodinger equation for time-dependent Hamiltonian is $$i\hbar\frac{d}{dt}\psi(t) = H(t)\psi(t) \, .$$ I know that the "instantaneous" solution of this equation is $$\psi(t+dt) = e^{-\frac{i}{...
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0answers
39 views

How to make an equal flow rate in 4 glass tubes with different inner diameters?

I would like to ask a question regarding a flow rate project I've been working on that required pneumatic software to solve. Unfortunately, I don't have the software, and I don't know how to control ...
3
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0answers
33 views

The definition of fidelity for fermion

The definition of fidelity for two mixed ensembles is $F=Tr\sqrt{\sqrt{\rho_1}\rho_2\sqrt{\rho_1}}$. Now I came across a problem in numerical calculation, Systems A,B are identical, but attached to ...
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0answers
29 views

Finding the initial state in the power method for Hamiltonian diagonalization

In section III of the lecture note Chapter 1: Exact Diagonalization, Weimer has described the Power method for Hamiltonian diagonalization. The process requires the choice of an random initial state ...
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32 views

Heliocentric Cartesian position of moons

I have a working Kepler orbit system that is GPU accelerated to allow precision, speed and parallelism and more importantly allow as many factors as possible in calculation. For various reasons I ...
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1answer
76 views

Finding explicit unimodular transformations for Chern-Simons K-matrices

An invertible, symmetric matrix with integer entries, $K$, that encodes the braiding and statistics of an Abelian topologically ordered state, is equivalent to another such matrix, $K'$, if there ...
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29 views

Implementing fixed-temperature, solid-wall boundary conditions

I wish to simulate the behaviour of a fluid along one dimension, where the right boundary is transmissive and the left boundary is a solid wall at a fixed temperature. Temperature is not one of my ...
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4answers
167 views

Schrodinger equation for time-dependent Hamiltonian?

Can I write a Schrodinger equation for time-dependent Hamiltonian like this: $$i\hbar\frac{d}{dt}\psi(t) = H(t)\psi(t)$$ and then perform Euler integration like this: $$\psi(t+\Delta t) = (1-\frac{...
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0answers
89 views

Why does the method below work?

Please explain why this method works. I get this idea when try to solve adiabatic gas expansion by using numerical method. The analytic/exact solution for the expansion will be $PV^\gamma$=constant. ...
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2answers
38 views

Data transmission in optical fibers

Im reading though my Network Architecture lecture notes and it states optical fibers need a repeater every >10km. Repeaters are used to amplify digital signals but the notes do not explain or state ...
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2answers
72 views

Which timestep should I use for a $N$-body simulation of the Solar system?

I am trying to implement a $N$-body simulation of the Solar system and I am stuck on the issue of the simulation timestep size. At first I would like to use a simple Euler stepping scheme. Knowing ...
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1answer
81 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 ...
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0answers
47 views

How are boundary consitions implemented correctly in time dependent hydrodynamics?

I posted this question more than one year ago and got an answer recently. This answer looks good to me, but indicates that something is wrong in my original approach to the problem. Can someone tell ...
3
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1answer
61 views

Collision between a “spring” and a particle

I am currently attempting to create a simple 2D physics engine, and I just need to know how to solve a certain collision. I have particles, and between any two particles, springs can be connected. ...
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0answers
42 views

How to calculate the string order parameter (for Haldane phase) in density matrix renormalization group?

The ground state of the spin-1 chain is the Haldane phase, which is known to be a symmetry protected topological phase and cannot be detected by conventional order parameter (beyond the Landau-...
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0answers
28 views

How Periodic Boundary Condition (PBC) is related to Band Structure of Quantum Dot?

I am reading about relationship between different lattices and their band structures.I have few questions about them: Q 1. Is is possible to find out band structure of a quantum dot (which is a ...
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0answers
23 views

Master curve of the 3D Ising model

I am currently doing some grand canonical Monte Carlo simulations for LJ particles and my professor has asked me to map the normalized probability distribution of density on to a master curve of the ...
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0answers
25 views

Mixed Neumann/Dirichlet BCs in Poisson-Schrodinger self-consistent solver

I'm currently in the process of writing a self-consistent Schrodinger-Poisson solver for a device heterstructure (High Mobility Electron Transistor). I am having a few difficulties however. It seems ...
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0answers
12 views

Computing the dynamics with a bilateral constraint in position

Let's says I have a dynamical system of generalized coordinates $x$, subject to a bilateral constraint $g(x(t),t)=x_1(t)-d(t)=0$ where $d$ is a prescribed displacement. I am looking for the ...
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1answer
97 views

Finite Difference Method (FDM) solution to heat equation in material having two different conductivity

I am not from a mechanical engineering background and I have not taken any courses in PDE so this may seem trivial for many. and I am writing a Matlab code with the objective to solve for the ...
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1answer
42 views

Laser resonator modes

For a resonator, plot the intensity as a function of time for (i) when the modes have identical phases, and (ii) when the modes have random phases. Attempt Here is the equation for intensity (p. ...
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29 views

Numerically integrate equations of motion with noise

Consider the equations of motion $$\begin{cases} \dot{x}(t) & = v(t) \\ \dot{v}(t) & = -\frac{\lambda}{m} v(t) + \frac{1}{m}F^{c}(x(t)) = a(x(t), v(t)) \end{cases},$$ where $x$ is the ...
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0answers
29 views

Keplerian orbits and radial velocities: problem with true anomalies

I am writing a pure Python code to calculate radial velocities of stars with massive objects orbiting them. I am following the formalism from Murray & Correia (2011) (hereafter MC11). In a given ...