# 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 ...
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 ...
32 views

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". ...
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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### 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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### 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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### 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 ...
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 ...
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 ...
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 ...
1k views

### 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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### 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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### 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 ...
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 ...
14k views

### 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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### 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, ...
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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### 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 ...
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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### 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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### 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 ...
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 \\ ...
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 ...
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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### 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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### 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 \...