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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.

0
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0answers
79 views

How to calculate the total resistance of a grid? [on hold]

I am trying to calculate the total resistance of a metallic grid between the points $y=0$ and $y=L$ where the black lines represent metal and white areas are insulators. This is how I would proceed: ...
0
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0answers
30 views

Diffusion between unequally spaced points?

I believe what I have is a rather simple issue at heart: assume I have a number of $M$ scattered points in an $N$-dimensional space $\mathbb{R}^N$. Each of these points has coordinates $x \in \mathbb{...
1
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0answers
24 views

Fourier transforms and convolution for finding Fraunhofer diffraction of compound objects: how does it work?

I've been exposed to this notion in multiple classes (namely math and physics) but can't find any details about how one would actually calculate something using this principle: Diffraction in optics ...
0
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0answers
16 views

How do I find information dimension using 2D wavelet analysis method in the Harfa Software? [closed]

I'm looking for help with the software Harfa. Specifically, how do I find the information fractal dimension and correlation dimension?
-4
votes
1answer
70 views

Brute-forcing the theory of everything [closed]

If brute force doesn't work, you're probably just not using enough of it. That's especially true for guessing combinations of stuff, like characters in a password. Assuming some combination of ...
0
votes
1answer
54 views

Spring-Mass system motion and eigenvalues [closed]

I'm trying to solve Lagrange differential equations of motion; where $L=T-U$. Also how can I use the output solution for each $x1, x2, x3,,,, xn$? Assume N=100. Here is my Code ...
0
votes
1answer
72 views

Can anyone tell me how can draw shadow of black hole like in presented in Intersteller movie? Is there any code for it in Mathematica or in Python? [closed]

Equation of motion for photon $$ \Sigma \frac{dt}{d\lambda} = aL\left(1-\frac{r^2+a^2}{\Delta}\right) + \omega\left(\frac{\left(r^2+a^2\right)^2}{\Delta}-a^2 \sin ^2\theta\right)\ , $$ $$ \Sigma\frac{...
2
votes
2answers
84 views

Wave simulation without reflection on the boundaries [duplicate]

I would like to numerically simulate a wave (let's say in a string) with different boundary conditions: Fixed endpoints Periodic Boundless $\varphi(x, t)$ is the value of the wave (vertical ...
0
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0answers
48 views

difficulty of lid driven cavity simulation

Many people do lid driven cavity simulation, but most people don't get correct results. Many wrong attempts give an overall spinning motion of the fluid, without corner vortices. What's the reason of ...
0
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1answer
29 views

FEM: Distributed loads over adjacent quadratic bar elements

I am an electrical engineering student trying to teach myself Finite Element Methods (FEM) through a couple of textbooks and independent study. While I believe that I understand the basic ideas ...
2
votes
2answers
64 views

How can I simulate a ground state degenerate system numerically?

I'm using numerical method like DMRG to simulate ground state of correlated systems. But the degeneracy of the ground state has long bothered me: When degeneracy exists the ground state isn't unique. ...
-1
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2answers
97 views

Can we create new physics through moderately brute force computing? [closed]

So my argument for this is that the expansion of knowledge in any field of physics depends on what is previously known, and what we physicists express or knowledge as equations. So here's what I ...
-1
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1answer
44 views

Would any continuous model of the universe have/be based on hypercomputational laws?

I've read that when Turing-Church thesis is applied to the universe and physics, one of the three interpretations that we can use and is defended by some important physicists is that: "The universe ...
1
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2answers
46 views

Clarification on the Lid-Driven Cavity Problem in CFD

I need some clarifications on The Lid-Driven Cavity Problem. What does it actually mean? I know cavities are bubbles created when a fluid moves through liquid in low pressure zones, but what does the ...
1
vote
1answer
18 views

Self consistent calculations in quantum well. Mixing by electron density?

I'm challenging the problem of calculating energy structure of InAs/GaAs quantum well. One part of the task is to perform self consistent calculations in order to include potential that comes from ...
0
votes
1answer
31 views

Bond order correlation function

I am trying to compute the bond order correlation function, $g_6$. It is defined based on the bond order parameter: $$\psi_6(x_i) = \frac{1}{N_i}\sum_{i=1}^{N_i}{\exp(i6\theta_i^j)}$$ where $\theta_i^...
2
votes
0answers
50 views

Would CTCs in wormholes change physical laws?

A wormhole is a speculative structure linking disparate points in spacetime, and is based on a special solution of the Einstein field equations solved using a Jacobian matrix and determinant. (https:...
1
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0answers
20 views

How to classify your fluid is a transitioning from a liquid to gas from numerical computation

I saw at one time that if the kinetic energy/potential energy of the gas was approaching 1 then the gas is becoming a liquid. I can't find the reference where I found that though (it was on stack ...
0
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1answer
28 views

Using FFT for spins in a non-cubic crystal lattice

Classical Ising/XY/Heisenberg models on a crystal lattice are commonly used to model magnetic materials. These can be studied using Monte Carlo simulations on a computer. Magnetic systems are often ...
0
votes
2answers
68 views

Big Data Handling at the LHC

My understanding is that much of the data that is is collected at the Large Hadron Collider is similar to that in the image below, and that a vast amount of the data contains little of specific and ...
1
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0answers
35 views

Energy required for computation [closed]

Is there a way to quantify a theoretical value for the minimum amount of energy required for arbitrary computation? Can an infinite amount of computation occur in a finite amount of time?
2
votes
2answers
105 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 ...
1
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0answers
40 views

Numerical exact diagonalization of tight binding Hamiltonian

I want to exactly diagonalize the following Hamiltonian for $10$ number of sites and $4$ number of spinless fermions $$H = -t\sum_i^{L-1} \big[c_i^\dagger c_{i+1} - c_i c_{i+1}^\dagger\big] + V\sum_i^{...
0
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0answers
40 views

Efficient numerical evaluation of Wigner function

Suppose we want to calculate the Wigner function of some state $|\Psi\rangle = \sum_{n=0}^{N_{max}} c_n|n\rangle$ ($|n\rangle$ are the eigenstates of the Harmonic oscillator) numerically. Starting ...
2
votes
0answers
19 views

How to set the number of fermions in the whole system in fermionic-DMRG program?

In infinite DMRG (density matrix re-normalization group) algorithm, we increase size of super-block by two sites in each iteration. How do we set number of fermions in the system? Let's say we want to ...
1
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1answer
81 views

Phase separation in physics

I would look to familiarize myself with the current literature of phase separation. If one can direct me to statistical/thermodynamics theories of phase separation. Has phase separation been ...
1
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0answers
45 views

How is Poisson's Equation solved numerically?

This question is of pure interest. I would like to know, how a mixed boundary value problem like the following can be solved numerically: Lets say I have two conducting plates (not necessarily ...
0
votes
0answers
55 views

How to calculate the Wigner function of $|n\rangle \langle m|$ for $n\gg m$

I know that this may seem odd, but suppose you want to calculate the Wigner function of the state $|n\rangle \langle m|$, where the states are the number states of the harmonic oscillator. One can ...
0
votes
2answers
47 views

In Wang Landau method, how can I avoid large entropy difference?

Summary: In Wang Landau method, you have to calculate the probability $\exp (- \Delta S)$ but $\Delta S$ is generally large when the size of the system is not small. How can I make $\Delta S$ small? ...
0
votes
0answers
48 views

Self-averaging quantities in physics

This question is about self-averaging quantities in physics. For a definition see: https://en.wikipedia.org/wiki/Self-averaging. For concreteness I give an example below. Example Consider a ...
1
vote
1answer
62 views

Math notation for heating object

An object with mass $m$ and heat capacity $c_{p}$ is exposed to heating $P_{th} $[kW] and thermal losses $\dot q$ [kW/°C]. The energy equation illustrating the process of heating it from $T_{max}$ to $...
20
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5answers
3k views

How do computers “solve” the three-body-problem?

I've done a bit of research, and have learned that computers "solve" the three-body-problem by using "Numerical methods for ordinary differential equations", but I can't really find anything about it ...
1
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0answers
70 views

How to deal with fermionic operators in density matrix renormalization group (DMRG)?

Let we have 1D Hubbard model with spinless fermions $$H = -t\sum_i^{L-1} \big(c_i^\dagger c_{i+1}+c_{i+1}^\dagger c_i\big) +V\sum_i^{L-1} n_i n_{i+1}$$ Though this model can be mapped onto XXZ ...
2
votes
1answer
35 views

What is this secondary transition in the simulation of the Ising model?

Here, the horizontal axis is the strength of the ambient magnetic field. The Hamiltonian I used is $$H = -h\sum_i \sigma_i - J\sum_{\langle i \, j \rangle}\sigma_i\sigma_j.$$ The horizontal axis is $h$...
1
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0answers
121 views

Fraunhofer diffraction problem in Python: How to interpret discrete Fourier transform (DFT) spectrum?

I have a periodic phase grating consisting of lenslets along the x-direction, invariant in y. I want to use python to calculate the far-field (Fraunhofer) diffraction pattern that one gets when ...
2
votes
1answer
49 views

Scaling Problem with Variational Method

$\def\braket#1{\langle#1\rangle}$ I am attempting to solve a particular Hamiltonian by variational method. The wavefunction that I have selected is as follows: $$ \Psi = Ne^{\frac{-kr}{2}}\sum_{i=0}...
1
vote
1answer
32 views

Vector Poisson Equation for a symmetrical geometry

I was recently doing some simulations involving the vector Poisson equation and symmetrical geometries with respect to one plane. My question is basically if the computations involved can be reduced ...
1
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0answers
61 views

Wolff cluster update in Monte Carlo simulation - at critical temperature [closed]

A general question to the Monte Carlo experts. When I use Wolff algorithm for global updates, say for Ising 2d, I always flip at least one spin (the initial random spin in the cluster). So, near the ...
0
votes
1answer
68 views

How can the analytical solution of the diffusion equation be used for a series of $N$ positions?

Given the exact solution to the diffusion equation: $$C(x,t) = \frac{1}{\sqrt{4 \pi D t}} \exp\left[-\frac{x^2}{4 D t}\right]$$ I am unsure as how it can be applied to a 1D series, as this equation ...
-1
votes
1answer
42 views

Non-linear optics - solve differential equations coupled with the finite difference method [closed]

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_{...
0
votes
0answers
18 views

Computational solution of exponential decaying wavefunction tail

As I am going through some (quite simple) computational physics exercices I have a question concerning one exercise that involves solving the radial Schrodinger equation. This is done with the ...
-1
votes
1answer
62 views

Numerical approximation of the wavefunction in a delta-potential [closed]

I am trying to approximate the wavefunction of a particle in a delta potential $U(x) = -U_0 \delta(x)$ with $V_0 \gt 0$. I am using the following formula to calculate the wavefunction: $\psi(x+\Delta ...
0
votes
0answers
41 views

Finding ground state energy using numerical real space renormalization group

I want to find ground state energy (as well as wavefunction) for spinless $tV$ model using Real-Space Renormalization Group (RSRG) approximation. The $tV$ model is defined as $$H=H_t+H_{int}=-t\sum_{i=...
5
votes
1answer
105 views

Is there any relation between density matrix renormalization group (DMRG) and renormalization group (RG)?

Probably I am going to receive many down-votes for this post but I really need to ask this question here. I am new to statistical mechanics. I wanted to learn Density Matrix Renormalization Group (...
2
votes
2answers
145 views

How can I explicitly express the Ising Hamiltonian in matrix form?

I am reading this book about numerical methods in physics. It has the following question: Consider the Ising Hamiltonian defined as following $$H=-\sum_ {i=1}^{N-1} \sigma_i^x \sigma_ {i+1} ^x + h ...
-2
votes
1answer
123 views

Putting high symmetry points labels to a band structure plot [closed]

So far I've got this plot using Quantum Espresso. I want to put gamma, X, L, etc labels to the k-path. Quantum Espresso's ouput states the following: ...
10
votes
2answers
315 views

How can one obtain the metric tensor numerically?

I am self-studying General Relativity. Is there a method for obtaining the metric tensor exterior to a specified mass distribution numerically? In the simplest case of a spherical mass this should ...
0
votes
1answer
45 views

Ising magnetization in metropolis

I am working on the Metropolis-Montercarlo algorithm for the square lattice ising 2D. Im running the simulations for a given lattice size, running from low temperature to high temperature, and ...
1
vote
1answer
57 views

Is numerical lattice wavefunction smooth? — graphene tight binding case

I tried to follow exactly Sec. II.K [page 112-113, Hamiltonian after Eq. (113)] of the standard Review of Modern Physics paper on graphene, which is a tight-binding model of a graphene stripe under ...
0
votes
2answers
81 views

Runge Kutta 4 for orbits and Newtonian Mechanics

How can I use the Runge Kutta 4 method to solve orbits of Newtonian Mechanics, with position vector $\mathbf x$, velocity vector $\mathbf v$ and acceleration vector $\mathbf a$? Do I still have to ...