All Questions

1,903 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
1
vote
0answers
444 views

How to solve nonlinear optimization with constraints that have singular jacobian

I'm solving a nonlinear constrained optimization with constraint of following form: $$\mathbf{A}^T\mathbf{A}-\mathbf{I}=\mathbf{0}, \mathbf{B}^T\mathbf{B}-\mathbf{I}=\mathbf{0}$$ where $\mathbf{A}$ ...
1
vote
0answers
94 views

Stability question (finite difference): dealing with corner nodes

Consider one initial boundary value problem for sphere. $$\frac{\partial u}{\partial t}=\operatorname{div}A\nabla u +f$$ Here is explicit numerical scheme (we consider that it is stable): $$\frac{u^{...
1
vote
0answers
155 views

Is it possible to generalize the two view Sampson error to multiple view cases in computer vision?

In multiple view geometry of computer vision, there is a geometric error called Sampson error which is very useful in the nonlinear estimation of fundamental matrix....
1
vote
0answers
129 views

Quadratic programming problem involving permutation matrices

Does anyone know a good algorithm for quickly finding an approximate solution to the following problem? Given two square matrices $A$ and $B$, minimize $\| P A P^\top - B \|$ over all permutation ...
1
vote
0answers
206 views

Characteristic length of differential element of cylinder surface?

I am trying to find the Nusselt number for a small element of the outside of a cylinder that has a height of $\Delta z$. I found the average Grashof number of a surface as $$Gr_{L}=\frac{\beta \rho (...
1
vote
0answers
188 views

Problem with cell size and boundary conditions in transient cylindrical conduction

I am attempting to model the steady state behavior of a cylinder using the finite volume method (FVM) subjected to a variety of boundary conditions in Matlab. First off, I am treating the cylinder as ...
1
vote
0answers
51 views

Size reduction of matrices in dispersion curve calculation

I have an energy dispersion curve obtained from the eigenvalues of $$E(k) = \text{eig}(T e^{ik} + T^H e^{-ik} + H_0),$$ where $H_0$ and $T$ are $N\times N$ square matrices, $T^H$ is the Hermitian ...
1
vote
0answers
86 views

Increase convergence of non-linear equations resulting from ODEs

I am trying to solve a set of couple ODEs: $V_l(r) - r W_l(r) - f1(r) W_l' = 0\tag 1$ $r^2 h''_l(r) + f2 r h_l'(r) + f3 h_l(r) - f4 U_l(r) = 0 \tag 2$ $\kappa (U_l + h_l) + V_{l+1} + W_{l+1} = 0\...
1
vote
0answers
350 views

Practical implementation of spatial binning for rectangular range queries

I have a bunch of polygons and a coarse uniform grid. I want to implement two different range queries, for a rectangle aligned with the uniform grid: Does the rectangle intersect with any polygon at ...
1
vote
0answers
73 views

Will Sumatra interfere with git?

As far as I understand, Sumatra does some sort of versioning of simulation scripts and output files. If I start to use Sumatra inside a git working directory, can Sumatra end up interfering with git ...
1
vote
0answers
1k views

Crank-Nicolson for 2nd- and 4th-order finite differences

I modeled the heat equation, $$ u_t = au_{xx} $$ using the common 2nd-order Crank-Nicolson scheme, $$ \frac{u^{n+1}_i-u^{n}_i}{dt} = \frac{a}{2\,dx}\left(u_{i-1}^{n+1}+u_{i+1}^{n+1}-2u_i^{n+1} + u_{i-...
1
vote
0answers
176 views

Numerically evaluate 1D inhomogeneous wave equation solution

I am trying to solve the following 1D inhomogeneous wave equation. Forgive me if I a miss any rigorous mathematical concept. $$ \frac{\partial^2 u}{\partial x^2} - \frac{1}{c^2}\frac{\partial^2 u}{\...
1
vote
0answers
85 views

Assignment optimization problem

I have to find a solution to a problem and I don't know where to start. Lets imagine I have a list of n containers and m processes. Each process resides already within a container and have 4 ...
1
vote
0answers
103 views

Quadratic optimization without any cross terms

I need to solve a quadratic program in Java which minimizes a sum of squares. The problem is that there are constraints to be satisfied, and so a quadratic optimizer must be used. I've been thinking ...
1
vote
0answers
41 views

Spectra of the energy flux VS transfer spectra?

In direct numerical simulation of turbulence what is the advantage to look at the spectra of the energy flux rather than the transfer spectra? The transfer spectra corresponds to the triple-velocity ...
1
vote
0answers
82 views

Issues with CVX package for optimization

I am trying to use the cvx package for optimization. However, I am having some issues with it. I have a variable X which is a matrix but I cannot add $X^{-1}$ in the objective function. What should I ...
1
vote
0answers
58 views

speckle interferometry (or other interferometry) software

This might not be the best place to ask, and if its not could someone please point me to where would be better, but here we go anyway. Does anyone out there know of open source software which can be ...
1
vote
0answers
249 views

Curvature of level-sets of CG1 function

Let us have simplicial mesh and continuous function $u$ which is piece-wise linear and non-constant on every cell. Then normal vector to level-sets of $u$ is given $$\mathbf{n}=\frac{\nabla u}{|\nabla ...
1
vote
0answers
58 views

discrete versions of Lp norm

The discrete analogue of the $L_p$ norm for the mesh function $V$ is $$\|V\|_{l^p(\bar{\Omega}^N)}=\left(\sum_{i=0}^NV_i^p\bar{h}_i\right)^{1/p}$$ where $\bar{\Omega}^N$ is an arbitrary mesh, $\bar{h}...
1
vote
0answers
2k views

Simulink PDE (MATLAB)

I need to build a system in Simulink that solves a PDE, but I can't find any literature or books where it is described how to do it (especially any stuff according to modeling PDE in Simulink). ...
1
vote
0answers
100 views

Hatree-Fock, reasons for convergence/ non-convergence

I'm new here so please forgive me if I lack proper stack exchange etiquette. So, I was wondering if anyone here could provide insight on a problem that I am running into with with a Hartree-Fock ...
1
vote
0answers
232 views

Block Backward Differentiation Formula (BBDF), on order 4 formula

I am trying to implement a program the numerical method to solve ODE called Block BDF as explained in this article: https://waset.org/journals/waset/v38/v38-49.pdf As it is variable step-size, I need ...
1
vote
0answers
55 views

Sine series using exponential based FFT

I have such a problem - I would need to expand a discrete function in a sine fourier series but I would like to use exponential based library for FFT (I will use CUDA to compute it). What have I to do ...
1
vote
0answers
30 views

Combining trend estimation and constrained Marquart fit

This title certainly needs some clarification: I need to compute parameters $a_i$ for a helper function $f(\vec{a};k)$ (for grid interpolation) which is fitted to a number of values $y_k$ which are ...
1
vote
0answers
260 views

Accurate force-field for MD

I am still a fairly new graduate student, and I am having trouble simulating a metal-organic framework. I am currently using UFF (I implemented it for LAMMPS), and it works well for some MOFs, but ...
1
vote
0answers
35 views

Simulation of asymmetric structures (occupancy = 0.5) unstable

I am trying to simulate a metal-organic framework in LAMMPS using the UFF potential. It's working quite well for some structures where all molecules have an occupancy of 1. However, when I have a ...
1
vote
0answers
66 views

Looking for a java library or algorithm for efficiently implementing the second Chebyshev function

Does anyone know of a java library or algorithm for efficiently implementing the second Chebyshev function? To be clear, I'm refering to this expression: $$\vartheta(x) = \sum_{p \le x}\log p$$ $$\...
1
vote
0answers
454 views

CUDA Mandelbrot Set effective bandwidth and optimization

I was reading through this article (very good article and excellent blog BTW) to do some measurements in my (very simple) implementation of the Mandelbrot Set. I'm using a Quadro 2000D card which has ...
1
vote
0answers
85 views

How to create synthetic data from known weights

I'm doing some machine learning where I have lots of data and through optimization I'm trying to learn the weights for the model. I'd like to check that my learning actually works correctly. For that ...
1
vote
0answers
219 views

Sign or cardinality constraint when solving for sparse signal

I'm currently learning about using linear and semidefinite programming to find sparse solutions to problems. In particular, finding sparse solutions where the sampling functions are sinusoidal (...
1
vote
0answers
363 views

features recognition & reconstruction of 3d mesh delaunay matlab

I managed to display the coordinates of x,y and z into a 3D mesh by using delaunay function. The coordinates are in .obj format actually and i have read it into matrix form. Now, i would like to ...
1
vote
0answers
937 views

Pixel-To-Angle Transformation in Camera Image

I'm trying to localize points I see in a camera image in terms of azimuth and elevation and match points between shots. Individual shots should differ only in rotation around the camera's center (...
1
vote
0answers
63 views

Can I use RANS to see the effect of mixed convection?

my question is: can I use a RANS simulation to see the effect of mixed/natural convection? Actually I have also a second question: I would like to do this in Comsol multiphysics, but it seems that it ...
1
vote
0answers
254 views

Memory allocation error with GSL ODE solver applied to system of 4 ODEs

I am trying to solve a (large) system of ODEs with GSL solvers. When I use driver method I get an error message of could not allocate space for gsl_interp_accel, ...
1
vote
0answers
28 views

PCA performed on a configuration with scaled axes

Suppose a configuration $X\in\mathbb{R}^{n\times 2}$ is output of PCA on some high-dimensional data $Y\in\mathbb{R}^{n\times h}$. Note that this PCA is performed by $$X=Y\cdot U,$$ where columns of $U$...
1
vote
0answers
165 views

Enforcing continuity conditions in pseudospectral domain decomposition methods for time dependent PDEs

I have a partial differential equation of the form $$ \frac{d}{dt}f(x,t) = \Theta(x) f(x,t) \qquad \Theta(x) \sim \left[\frac{d^2}{dx^2} + k^2(x)\right] $$ subject to $f(x,t=0) = f_0(x)$, and $f(x=0,t)...
1
vote
0answers
500 views

How to solve advection equation using semi-lagrangian method?

I am working on something that involves solving an advection equation $\partial{x}/\partial{t}+\vec{u}\cdot\nabla{x}=0$ in 3D. I discretized the space into 3d cartesian grid and used the Semi-...
1
vote
0answers
144 views

Determine set of dividend and divisor for quotient

I have the following Problem: I know the range within the results of a division must lie. [ quotientrange ] Additionally, the quotient should not exceed a certain number of fractions. I know, that ...
1
vote
0answers
84 views

Proportional equality constraints

Consider a node $s$. Let's assume that there are three outgoing arcs from node $s$ namely $(s,i)$,$(s,j)$ and $(s,k)$. Corresponding to each of these arcs, there is a flow proportion value $t_{sj}\in (...
1
vote
0answers
100 views

Anisotropic cover with n-cuboids

I'm working on an algorithm for which I would like to cover an $n$-dimensional unit cube by a set of $n$-cuboids (i.e., $n$-dimensional rectangles). The size and orientation of these cuboids is ...
1
vote
0answers
81 views

Constraint solving over modular domains

I have a set of constraints over modular domains e.g. $\exists a \in A_i : x \equiv a \pmod{n_i}$ for all $i=0,\ldots,k$ The question is, does such an $x$ exist? I've been pointed to method of ...
1
vote
0answers
58 views

Assembled human ESTs for annotation

I am annotating protein-coding genes in a region of the human genome and am looking for a set of assembled ESTs I can use as evidence for constructing gene models. A quick search of NCBI's SRA shows 4,...
1
vote
1answer
175 views

GPU libraries for integer matmul | overflow tolerated

Are there any high performance integer BLAS libraries that implement matrix multiplication i.e. i32gemm and i64gemm ? I need to use them for a cryptographic application and can tolerate overflows, i.e....
1
vote
1answer
794 views

lapack singular matrix

I'd like to find a condition that allows me to determine if a matrix is invertible or not. naively, I computed the determinant to see if it was zero. but then I realized that even for very small ...
1
vote
1answer
339 views

Eigenvalue problem with periodic boundary conditions: Are my eigenvalues correct?

I am using a (central) finite difference scheme to solve the eigenvalue problem $$-\frac{d^2}{dx^2}u = \lambda u$$ with periodic boundary conditions on a unit interval. I use arpack's zndrv1 and ...
0
votes
0answers
63 views

How to debug segmentation faults in large problems?

I am sorry if this question seems like off topic or opinion based, but I was not sure how to go about it. I am currently working on a 100k x 100k positive definite linear system and trying to solve it ...
0
votes
0answers
49 views

4th Order Adams-Moulton Method C++

I am trying to solve an ODE using 4th Order Runge Kutta and the 4th Order Adams-Moulton Method. I iterate over a couple of thousand timesteps and it seems to hold fine when the values are constant(...
0
votes
0answers
49 views

FEM Meshing artifact at nodes with fewer neighbors

I wrote a 2D-FEM solver to solve some diffusion process and wanted to verify my code with a test problem. The input was $f(x,y) = x^2+y^2$ and I applied the stiffness matrix on it to get $\Delta f = 4$...
0
votes
0answers
29 views

Numerical simulation for a bounded process. Is slight deviation a “normal” fact?

Suppose I have to numerically simulate a process $\{y_t\}$ such that $y_t\geq0$ $\forall t\in\mathbb{N}$, with $t$ denoting time-step. Let's suppose I use MonteCarlo with $\mathscr{N}$ simulation ...
0
votes
0answers
19 views

Scale of x-axis for Fourier transform

Consider a function $f(t)$ and its Fourier transform $F(\omega)$. The amplitude of the Fourier transform $F(\omega)$ depends on the frequency $\omega$ and thus also depends on the scale of the $t$-...

15 30 50 per page
1
30 31
32
33 34
39