Questions tagged [algorithms]

For questions about an algorithm as it relates to physics. DO NOT ask how to implement an algorithm, questions like that belong on Stack Overflow or Computational Science. DO NOT ask about the efficiency of an algorithm, or other such questions, questions like that belong on Computational Science.

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How to actually find a Hartree-Fock ground state?

I am interested in finding the Hartree-Fock ground state for a system of interacting fermions (with totally local scattering, so a delta-function interaction potential). I have read through some ...
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1answer
27 views

Metropolis Algorithm Transition-Proposal Probability

I'm working my way through a short section on the Metropolis algorithm in the lecture notes on Computational Quantum Physics by Prof. Troyer. However, I am not sure what probability distribution was ...
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1answer
32 views

References about “neutronic” algorithms

I am looking forward to apply for an internship in 5 months and I looked up the Jobs offers from last year, and some of them asked for a candidate with knowledge of "algorithms applied to neutronics". ...
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23 views

Winner-takes-it-all algorithm in particle decays

How does the winner-takes-it-all algorithm work for two competing processes, specifically in particle decay processes? What are its advantages against veto algorithm, for example?
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1answer
74 views

Modification of the Verlet algorithms for the pendulum problem

I'm trying to write a program to integrate the motion equations of the pendulum in the damped and forced case, that is, following this equation: $$ \frac{d^2\theta}{dt^2}=-\frac{g}{L}\sin(\theta)-\mu\...
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34 views

Fluid simulations on spherical coordinate grid: How to handle $\theta=0$ axis?

I am working on a fluid simulation code written in spherical coords. Whoever wrote the original didn't do a great job with the boundary conditions at $\theta=0$ and $\theta=\pi$ axes. My task is to "...
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22 views

Veto algorithm in particle decays and Monte Carlo techniques

What is the main concept behind Veto algorithm and how does it contribute to efficiency in Monte Carlo methods like when used in designing a parton shower?
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Method to build a polyhedral die with given probabilities [closed]

Let's define a die as a polyhedron that, if rolled over a perfect horizontal plane, ends up being in a physically stable unambiguous state labelled $n$. The die has $N$ states. Each state $n$ has a ...
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Numerically Solving EM problems. Book covering: ABS, PML, Near field calcul., LU fact, BicGstab, Pardiso etc

I looking for a book (or two) covering a range of topics: numerical implementation of boundary conditions (PEC, PMC, ABS); perfect matching layer; LU factorisation; numerical solvers and when to use ...
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1answer
47 views

State of $N$-body system after time $t$ (elastic collision & no gravity)

I am creating a gas particle simulator based game. All nodes (green circles) represent gaseous particles and collide elastically. My algorithm correctly accounts for two-particle collisions, as the ...
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141 views

$N$-body gravity simulator: why does energy conservation break down when introducing an adaptive timestep?

I am playing with an N-body gravity simulator using the velocity-verlet algorithm. In the actual simulation I normalize everything so that it is nicely behaved numerically, but I'll express things in ...
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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=...
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What the difference is between Størmer Verlet and regular Verlet method?

I was wondering what the difference is between the Størmer Verlet method and the regular Verlet method, if there is any.
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Using a time-like boundary as a computer?

Question and Summary Using classical calculations and the Robin boundary condition I show that one calculate the anti-derivative of a function within time $2X$ (I can compute an integral below) $$\...
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1answer
83 views

Is photon interference really random? [closed]

I know that according to the many worlds interpretation, there is no randomness and rather there is a universal wave function that simulates an observer with a continuously branching timeline. My ...
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1answer
71 views

Could you use the Barnes-Hut algorithm iteratively— with multiple center quadrants?

I was wondering if you could use Barnes-Hut simulation beyond what it was originally intended to be. For many Barnes-Hut algorithms, the forces are only considered for a single quadrant, the centroid, ...
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186 views

Using the Kalman filter given acceleration to estimate position and velocity [closed]

I am reading data from an accelerometer. I want to use this data to estimate velocity and position. Originally, I performed a double integration of acceleration to read this data, and as confirmed by ...
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2answers
249 views

Shor's algorithm with adversary - can (delayed) erasure of value qubits cripple calculations?

Let's look at quantum subroutine of Shor's algorithm: Hadamard gates create superposition of all (exponential number) values for input qubits. Then we perform a classical function on them, which is ...
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Have there been any patented physical models or computational algorithms? [closed]

There was a recent question (linked below) on the Law SE about the potential to patent algorithms. It appears there is a lot of gray area in the subject. Of course natural laws cannot be subject to ...
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verlet/leapfrog method lorentz force application

So I ll use leapfrog/varlet algorithm to calculate the trajectory of the particle In leapfrog method for initial values we need $v_{-1/2}$ and $x_0$. Hence I can write $v_{-1/2}=v_0-Δt/2a_0$ $v_0$ ...
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1answer
66 views

Time for Quantum Computational Prime Factorisation

I ran into this graph where the red one is $$x^3$$ and represents the number of steps as a function of factorised bits for a quantum computer. The blue graph represents the classical computer and has ...
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92 views

What is order of the Wolff Cluster algorithm?

What is the order of the Wolff Cluster update algorithm for Ising Model 2D and 3D?
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2answers
303 views

How to calculate the maximal Lyapunov exponent(s) of a multidimensional system?

I've been reading up about Lyapunov exponents for a university group project on chaos theory and I'm a little confused as to how they are calculated for a system of multiple dimensions. From what I ...
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1answer
69 views

MEMS gyro measured angular velocity vector

Notations I use: Consider a world frame $\{O_0, \vec{i}_0, \vec{j}_0, \vec{k}_0\}$ coordinate system and a rigid body $B$ with a coordinate system $\{O_1, \vec{i}_1, \vec{j}_1, \vec{k}_1\}$ attached ...
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1answer
322 views

Adiabatic QC: are there known difficult problems with spectral gap not exponentially decreasing?

Adiabatic quantum computers require slow evolution to maintain global minimum: $O(1/g^2)$ time, where $g$ is spectral gap: distance between two lowest energies. The danger is that this spectral gap ...
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1answer
184 views

Quantum Approximate Optimization Algorithm

I try to understand the 'Quantum Approximate Optimization Algorithm' (QAOA) by Farhi et al. - arXiv:1411.4028. I understand that the solution is hidden in the unitaries, but I do not understand how ...
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Shor's algorithm - why doesn't the final collapse of the auxiliary qubits cripple the computation?

Let's look at quantum subroutine of Shor's algorithm (image source): Hadamard gates create superposition of all (exponential number) values for input qubits. Then we perform a classical function ...
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1answer
58 views

Markov Process in Monte Carlo simulation

I am trying to understand the detailed balance condition precisely. To get it I went on this page : https://cs.adelaide.edu.au/~paulc/teaching/montecarlo/node22.html It is written the following : ...
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1answer
73 views

What does “given one application of a black box” mean, in a quantum-computing context?

From Kaye, Laflamme and Mosca's An Introduction to Quantum Computing: Exercise 7.1.1 (Bernstein-Vazirani problem) Show how to find $\mathbf a \in Z_2^n$ given one application of a black box that ...
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163 views

Shor's algorithm - its causality and similar exploitation of QM?

Shor's algorithm is rather the most interesting quantum algorithm as it shifts a problem which is believed to need exponential classical time, to polynomial time for quantum computer, additionally ...
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6answers
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Could a computer unblur the image from an out of focus microscope?

Basically I'm wondering what is the nature of an out of focus image. Is it randomized information? Could the blur be undone by some algorithm?
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1answer
366 views

How do I use Kepler's Laws to propagate an orbit for a Two-Line Element (TLE) Set?

I need to propagate a large number of orbits (get a satellite's position at a certain time) from TLEs (two-line element sets) using Kepler's laws. Ordinarily I'd use a real propagator like SGP4/SDP4, ...
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1answer
112 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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3answers
182 views

High Energy Physics Algorithms in GEANT4

I have been learning to use the GEANT4 software and I came across the following statement in the Users Guide, and I couldn't help being curious as to why this was? I'm primarily a mathematician, so I ...
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3answers
274 views

Where is a classical computer better than a quantum one? [closed]

Where is a classical computer better than a quantum computer? Is there any known domain where classical algorithms always beat quantum ones, say, both in terms of time and space complexity? If yes,...
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1answer
169 views

Calculating the temperature in Creutz algorithm

Creutz algorithm is, as far as I know, a less popular Monte Carlo algorithm than the Metropolis algorithm - both are statistical mechanics algorithms. In one of his papers, Creutz shows his algorithm ...
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1answer
100 views

Assumptions in the proofs for the optimality of Grover's Search Algorithm

I was trying to understand this paper in which it is proved that Grover's search algorithm is optimal. On page 4, beginning of section 2 of the paper the author says the following In the proof I ...
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55 views

Using quantum state tomography in quantum search algorithms

Problem statement: The search space A involves elements $|0\rangle $, $|2\rangle$... $|d-1\rangle$. An oracle is provided for the function $f(x)$ where \begin{align} f(x)&=1 \quad x=x^{'}\in A \\ ...
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1answer
196 views

Test Deutsch's algorithm with constant function $f(x) = 1$

I am really, really beginner to QP. But for some reason, I am studying about Deutsch-Jozsa algorithm, and I have found this article which really helped me with understanding the pipeline of the ...
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105 views

Two dimensional plasticity with radial return

What is the proper method to scale deviatoric stresses back to the yield surface in plane stress 2D? I cannot get the radial return method to produce the desired results under plain stress conditions ...
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1answer
138 views

While solving 2D Poisson's equation, how to apply floating boundary at two edges, and Dirichlet at other two?

I have a square, at left and right edge of it; I exactly know the boundary values (Dirichlet boundary). But at top and bottom edge, I want to let the potential to float. That means I don't imply any ...
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1answer
89 views

How to simulate gravitational interaction of bodies in space?

I want to try simulating some bodies in space using the basic formulas I learned in my college mechanics class. So I know Newton's Law and some basic mechanics equations: $\vec{F} = G\frac{m_1m_2}{r^...
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1answer
386 views

Explanation of relaxation method for Laplace's equation?

Currently reading through Introduction to Electrodynamics (4th Edition) by Griffiths. I'm trying to wrap my head around Laplace's Equation, here are a couple quotes that I'd like to understand a bit ...
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Computational complexity - Quantum system [closed]

I have created a genetic algorithm to solve for the ground state of an arbitrary Hermitian matrix. it does this by working out fitness values which i have defined as -E = -$<\psi|\hat{H}|\psi>$. ...
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0answers
94 views

Quantum machine learning and exponential compression

There is a statement related to Quantum Machine Learning video lectures in which I get stuck. The explanation is derived from Seth Lloyd class. https://www.youtube.com/watch?v=Lbndu5EIWvI He starts ...
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1answer
517 views

Deutsch-Jozsa Algorithm for Non-Balanced+Non-Constant Functions?

Note: I'd imagine this will be a simple yes/no question for people better versed in this topic than myself, but nevertheless I'll provide a bit of background first for the edification of anyone who ...
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1answer
419 views

Baseline correction algorithm for Raman spectra. Raman baseline removal

Can someone please help with baseline correction algorithm? My task is to build an algorithm that normalizes baseline of spectrum WITHOUT using any additional software like Mathematica etc. I have a ...
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0answers
61 views

Matching measured eigenvalue of a matrix [closed]

Given a Matrix of the form below, we have 8 variables, $\omega_{i}$ and $J_{ij}$. we want to diagonalise the Matrix to obtain values to match the observed Eigenvalue in an Experiment. i.e. $\bar{\...
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45 views

What does the quantum behavior of indivisual in the Particle Swarm Optimization (PSO) algorithm means?

I am not specializing in physics,is it possible to explain; in simplified manner, what does the quantum behavior of individuals (particles) in the Quantum Particle Swarm Optimization (QPSO) algorithm ...
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1answer
83 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 \...