# 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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### Checking inverse metric and Christoffel symbols for the Kerr metric against references

I am trying to cross-check the Christoffel symbols and other very laborious geometric components in several metrics. In particular the Kerr metric is notoriously complex and results in expressions ...
• 159
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### Force-simulation for graph layout: How to avoid particle collapsing into a single point?

In a force-based graph-layout simulation using Barnes-Hut, what are the conditions for collapse? With collapse I mean multiple (or even all) nodes "collapsing" into a single point. Is there ...
• 1
1 vote
22 views

### Any quantum Monte-Carlo algorithm for calculating the lowest eigenenergy in each symmetry sector?

Suppose we have a hamiltonian which has the parity symmetry (e.g., the Heisenberg model with the open boundary condition). Is there any quantum Monte-Carlo algorithm which can be used to calculate the ...
• 1,957
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### About how to calculate observables in Quantum Monte Carlo with complex weights

I'm rewriting a Diagrammatic Quantum Monte Carlo algorithm following Werner, P., Oka, T., & Millis, A. J. (2009). Diagrammatic Monte Carlo simulation of nonequilibrium systems. Physical Review B, ...
• 165
54 views

### Is there a proof for critical slow-down in Monte Carlo?

It is physically understood why the standard Metropolis-Hasting algorithm slows down near the critical temperature, since it doesn’t utilize the divergence of the correlation length. However, I’m ...
• 2,123
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### Is Quantum State Tomography (QST) an inherently supervised or unsupervised problem in Machine Learning?

I am studying how to apply neural networks to the problem of Quantum State Tomography (QST) and I got confused when it comes to decide if this is a supervised or unsupervised learning problem. At ...
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51 views

### Understanding chapter 3.1 (Laplace's equation) in Introduction to electrodynamics Griffiths 4 ed [duplicate]

I really need help to understand chapter 3.1. What is the method of relaxation? How can I use the method of relaxation to solve Laplace's equation? How can I use the first and second uniqueness ...
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### How to efficiently calculate the inverse of the overlap matrix?

Now, we consider a non-orthonormal basis: $$\mathcal{S}_N=\{|\alpha\rangle,a^\dagger|\alpha\rangle,a^{\dagger 2}|\alpha\rangle,\ldots,a^{\dagger N}|\alpha\rangle\},$$ where $|\alpha\rangle$ is the ...
• 23
1 vote
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### Fringe pattern and ripples in the fringe visibility plot from interferograms

I am using a lens testing interferometer, where I record 4 to 5 interferograms with a 90$^{\circ}$ phase step between consecutive interferograms. In addition to the interferometer, I have also created ...
1 vote
77 views

### Simplest quantum Monte-Carlo method for the Bose-Hubbard model

I want to use quantum Monte-Carlo results to benchmark an algorithm for the Bose-Hubbard model. There are so many QMC methods in the market, so which one is the simplest one? I want the ground state ...
• 1,957
61 views

### How are the boundary conditions given in the SIMPLE algorithm on a forward staggered grid for a lid driven cavity flow?

I have a code given by my professor in which he applies the boundary conditions for the lid driven cavity flow. All the enforcement of boundary conditions I have seen elsewhere completely differ from ...
121 views

### Numerically computing induced magnetic field from current density

Let's say we have current density $J_i$ on a discretized grid with $(N_x \times N_y \times N_z)$ points. What is the best procedure to compute the induced magnetic field $(B_i)$ from the current ...
• 23
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### What are the advantages of tensor network algorithms over monte-carlo simulations in terms of time-evolution?

I understand that tensor networks and monte carlo simulations are based on completely different principles. However, to my knowledge both are used to simulate the time evolution of a system. Is there ...
• 325
1 vote
39 views

### An example problem to solve using 100 qubits?

Suppose we have in our possession 100 pairs of electrons. Each electron A1 - A100 is entangled with its respective twin B1 - B100. Each entangled electron pair has been set up to have opposite spins (...
• 593
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### Grover's algorithm & using wave interference for computing

Grover's quantum search algorithm contends that it is possible to search for a specific item in an N-sized unsorted database in only $\sqrt N$ attempts. Classically, it takes N/2 attempts on average ...
• 593
100 views

### Sensor Array Position Calibration in Anisotropic Media

Problem. I have a sensor array consisting of $n \gg 4$ receivers at unknown locations $\langle x_n, y_n, z_n\rangle$ embedded in an anisotropic medium whose index of refraction varies as a known ...
• 799
1 vote
113 views

### Why are time-reversible integration algorithms in molecular dynamics simulations favorable?

I read that integration algorithms that are not time-reversible tend to be less "stable". Where stable means that the total energy stays constant (is conserved). I'd like to know what it ...
37 views

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1 vote