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.
1,637
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Superposition states in an infinite square well
I'm trying to simulate superposition states in an infinite square well using Python, but my results don't match those from a web simulation.
I'm using the wavefunction and energy level functions ...
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How to properly compare DMRG results with analytical results?
In section III of arXiv:1711.09099 the authors implement the Hamiltonian in Equ. 12,13,14,15 via DMRG, the Hamiltonian is of the typical form as usual in quantum chemistry:
$$H=\sum_{i,j=0}^{d-1} h_{i;...
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How can I estimate the drag of a CAD model?
I have a CAD model that I’m trying to optimize for hydrodynamic-ness, programmatically (preferably with Python).
Is there a way I can find or estimate the drag force of the model, without having the ...
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Numerical model of 1D equations for compressible flow
The equations for 1D compressible flow are
$$\frac{\partial u(x,t)}{\partial t}-A\frac{\partial v(x,t)}{\partial x}=0,$$
$$\frac{\partial v(x,t)}{\partial t}-B\frac{\partial u(x,t)}{\partial x}=0,$$
...
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Seeking for advice for studying of computational material science [closed]
I am studying material science and I want to equip myself with the ability to conduct research through computational methods (particularly, I want to learn about VASP). I have studied calculus and ...
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How to find amount of energy which goes to heat in a system of damped springs in a gravity field?
I am writing a simple computer simulation of a system (in 2 dimensions), with several circular bodies. They all affect each other by their gravity and some of them are connected via damped springs (...
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Smoothed particle hydrodynamics for solving diffusion equation
I'm a novice to the smoothed particle hydrodynamics method and I'm keen to know how it can be used to solve partial differential equations. In particular I want to know how to discretize the spatial ...
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1
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Standard deviation of kinetic energy approaches average kinetic energy
I have a simulated system of lots of particles modeled as circles moving in 2 dimensions. They bounce off each other and off of walls. Momentum and kinetic energy are conserved.
I noticed that the ...
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Numerators in LoopTools
I want to calculate the diagram
$$ \int \text{d}^D q \frac{q_\mu q_\nu q_\rho q_\eta}{(q^2-m_1^2)((q_1+p_1)^2-m_2^2)((q_1+p_1+p_2)^2-m_3^2)((q_1+p_1+p_2+p_3)^2-m_4^2)((q_1+p_1+p_2+p_3+p_4)^2-m_5^2)} $$...
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1D Wave equations other than sinusoidal waves which can be graphed on Desmos Graph
I want to see waves equation other than the usual sine waves (or damped sine wave).
Im especially interested in graphing them on Desmos.
I have searched but everywhere either $sin(kx-wt)$ is shown or ...
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Visualizing 3D Lissajous curves
Lissajous figures are generally 2 dimensional, i.e. X and Y. But if an oscillation along a third axis Z (normal on the XY plane) is introduced, how would the resulting path look like? is there any ...
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Wick's contractions
According to Wick's theorem, we have
$${\left\langle {T\left[ {\hat A\hat B\hat C\hat D} \right]} \right\rangle _0} = {\left\langle {T\left[ {\hat A\hat B} \right]} \right\rangle _0}{\left\langle {T\...
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Difficulty solving conformal-bootstrap-like crossing equations using semidefinite-programming (SDP) via SDPB software
My question involves semidefinite programming (SDP) in the sense of attempting to find some vector $\alpha^{\mu}$ that satisfies the following conditions:
Normalisation: $\alpha^{\mu}n_{\mu} = 1$
...
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Why am I wrong when calculating the atomic system's stress?
Assume a static non-periodic-bounday-condition $N$-atom system in a cuboid box only have potential energy $U$, which is merely the function of all atom positions, i.e.,
$$U=U(\{{r_i}\}) \tag{1},$$
...
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CFD Boundary condition: Pressure far field vs Pressure outlet
I’m confused about a Pressure far field and Pressure outlet boundary condition
Should I be using a pressure far field (for the ‘outlet’ of the computational grid) instead of pressure outlet?
Flow is ...
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Nuclear level densities and neutron stars
My current PhD. project involves working with nuclear level densities (NLDs). However, I am more interested in the applications of NLDs to astrophysics. I know they are important to in calculations of ...
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What numerical methods can be used to verify the accuracy of Feynman diagram results?
Recently, I have been attempting to replicate the Feynman diagram calculation which was featured in an article here.
\begin{align}
&C_{x y x y}^{1, e}(i \Omega)= -(1-\delta) r_0^{-\delta} 2^{4+\...
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Solving Poisson equation for galaxy rotation curves
Can someone point me to the numerical methods to solve the Poisson equation for the galaxy rotation curves?
I've heard of some tools like PETSc or OpenFOAM. But I'm not sure if these are the right ...
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How does numerical simulation of GR work in the case of closed timelike curves?
In all cases I'm aware about so far, when you want to do a numerical simulation of a physical system, you invoke the initial conditions and program how the system evolves in time.
Now presumably, I ...
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Potential field in inhomogeneous conductor boundary conditions for Finite Volume Method
I have a question on how to represent a region of perfect conductance in a finite volume method solving the potential field inside a domain. To ask the question I will first explain the full situation....
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Geodesics: Energy functional vs length functional
The Wikipedia article about geodesics talks about the equivalence of obtaining the geodesic by either minimizing the length functional $L$, or by minimizing the energy functional $L^2/2$, cf. the Phys....
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What happens with tight boundary conditions in the V-CYCLE while doing numerical Electrodynamics
My problem is very simple to understand. We are trying to solve the Laplace equation in a domain that has sufficient boundary conditions to converge to some solution.
Our example is this.
2 ...
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Statistics error limit on a fitting
We are trying to analyze gamma-ray spectra that come from a neutron scattering in the soil sample. Our hope is to find the final error in the fitting parameters of the peak, which should look like a ...
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Gravitational acceleration in my acceleration data (IMU)
I am trying to do gait analysis and remove gravitational acceleration ($9,81 m/s^2$) from my data.
I have used IMU (on the patient's lower back) to record acceleration, angular velocity and roll/pitch/...
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Nonequilibrium Greens function via a DMFT-mapped Anderson model?
Let $H = \sum_{<i,j,\sigma>}t_{i,j}c^\dagger_{i,\sigma} c_{j,\sigma} + h.c. + U \sum_i n_{i,\uparrow}n_{i,\downarrow}$ be a standard Fermi-Hubbard Hamiltonian. Let us single out one site of the ...
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Is numerical optimization useful in (highly nonlocal) Lagrangian dynamics?
It is well known that many equations of physics can be formulated as an extremalization principle, i.e. that the equations arise from an action $S = \int L(t,x(t))dt$ with a time-dependent Lagrangian $...
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Looking for the name of this function? [closed]
$$2\Delta\frac{\sin(2\pi\tilde{\nu}\Delta)}{2\pi\tilde{\nu}\Delta},$$
$\tilde{\nu}$ is wave number (1/cm), $\Delta$ some constant (no units).
Is this just a sinc function scaled by $2\Delta$, or does ...
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How to plot spherical geodesics in the Kerr metric in maple?
I need to plot geodesics in the Kerr Newman Nut metric, but to do that I need to understand how to build geodesics for an already known Kerr metric in maple. I understand that in order to build ...
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Verlet algorithm without initial conditions
I was working on a problem asking 'in an oscillation of a bond in a single O2 molecule with a pair-wise Lennard-Jones (LJ) potential how does the total energy $E$ vs $t$ change?' it goes on to provide ...
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What are astrocentric co-ordinates?
A program I am using requires the ecliptic astrocentric cartesian coordinates of the Earth and the Sun in AU however I have never come across these co-ordinates before and the internet doesn't provide ...
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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 ...
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Connecting asymptotic scattering solutions to short-distance numerical potentials
Problem
I'm dealing with a one dimensional quantum mechanical scattering problem in a finite region, say $x\in\left[0,L\right]$. At first, this problem is defined as a finite-difference problem, i.e., ...
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How to solve the eigenvalue problem of Matrix product operator (MPO) using Tensor network method?
I am new to the Tensor network approach. I need to solve the eigenvalue problem for a Matrix product Operator (MPO). What are some techniques, resources, softwares or packages available to do it? I am ...
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Quantum State Tomography with Machine Learning [closed]
So, I am new to this area. I know a little bit on Machine Learning and Neural Networks and I'm a Physics student and recently I started studying Quantum Information Theory.
I found some papers and ...
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Electromagnetism for finite element simulations
I want to learn about electromagnetism, as I will need to run (time dependent) finite element simulations regarding electrical motors for my job. I only had one course in EM a long time ago, and I can ...
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Stroboscopic map
I am trying to plot the stroboscopic map of the classical kicked rotor, which is characterized by the equations:
$$p_{n+1} = p_n - \frac{dV}{dx}|_{x=x_n}$$
$$x_{n+1} = x_n +p_{n+1}$$
where $x_n$ is on ...
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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 ...
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Polynomial regression with microlensing parameters
As a hobbyist I would like to learn more about microlensing by exploring some data and performing some simple regression analysis. Based on the exoplanet archive of microlensing planets
https://...
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How to find a modelling function?
I have a list of boundary conditions, inequalities and general facts about a real world scenario involving probability distributions that evolve according to some parameters, but I'm struggling to ...
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How to solve the trajectory equation using quadratic drag formula?
I am doing a project on ballistics and projectiles and I was reading this link here and it states that the ballistics equation cannot be integrated analytically, and has to be integrated numerically. ...
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Can I do anything instructive by simulating QED on a lattice?
For learning something about the degrees of freedom and underlying path integral math, is it possible to do some kind of scalar QED or normal QED simulation on a lattice in the same way Lattice QCD is ...
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Understanding equations of motion for mass around Schwarzschild black hole
I want to create a program that simulates general relativity 2 body problem.
I am trying to understand the following equations of motion for mass around Schwarzschild black hole which are taken from ...
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Supernovae apparent magnitude in a simplified LCDM model
I want to generate some fake apparent magnitude of supernovae Ia at different redshift using the LCDM model and the fiducial absolute magnitude of supernovae Ia (-19.35) and I want to compare it with ...
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2
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Simulating rigid body collisions in 3d
I have been reading about physics engines and I am confused on how one approaches simulating collision responses.
I read about the coefficient of restitution:
https://en.wikipedia.org/wiki/...
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How to find equilibrium rpm of a wind-turbine / free-spinning rotor (using BEM)?
Background: I want to design a rotor-recovery system, which uses a free-spinning rotor to slow a fall instead of a parachute for example. From a mechanics and aerodynamic standpoint it should work ...
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Normalization in tensor networks [closed]
I am trying to implement the iTEBD algorithm for the $PXP$ model, i.e, the hamiltonian is
$$H = \sum_iP_{i-1}X_iP_{i+1}.$$
Here $P$ is the projector onto the ground state and $X$ is the usual pauli x ...
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Why does Ronald Ruth integrate momentum as velocity in his 1983 paper "A canonical integration technique"?
I am trying to apply a time integration technique for a system of discrete particles using Hamiltonian symplectic mechanics.
In his relatively well-known paper (CERN,PDF) on symplectic integrators, ...
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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 ...
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EinsteinPy--how does one plot the output of a single element of a tensor with respect to multiple coordinates? [closed]
I would like to plot a component of the Einstein tensor from a metric computed in EinsteinPy. In order to get this metric, I used einst=EinsteinTensor.from_metric() ...
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Where does the relation between simulation time and mesh step size for FDTD simulations come from?
I am using Lumerical FDTD solutions to simulate a planewave through a region of space and some of my analysis requires me to know the relation between the simulation mesh step size and the time taken ...
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