0
votes
0answers
6 views

Collocated Grid Navier Stokes Solver

I want to solve Navier Stokes equations on a collocated grid. Earlier, I was using a MacCormick scheme based solver where I discretized predictor step in forward differences and corrector step in ...
0
votes
0answers
15 views

Are Their Relationships Between Knowledge Management and Ontologies? [on hold]

I'm working on a research project to develop an ontology for wetlands in PROTEGE, but I have doubts about the relationship between ontologies and knowledge management, I understand that ontologies are ...
0
votes
1answer
14 views

How to plot selection over time for only components, but not magnitute. of a vector in paraview?

I am doing a time evolution analysis for a structure and have already got the displacement result, which is a vector including x and y components. And I want to plot the time evolution of x and y ...
1
vote
1answer
56 views

conservative v non-conservative

I have always come across the terms "conservative" as opposed to "non-conservative" forms of equations in fluid mechanics. Is there a good reference that someone can share to clearly distinguish the ...
0
votes
0answers
47 views

Integer programming with Matlab

I'd like to know how to solve in MATLAB the following integer optimization problem : $\underset{B,D}{\arg\min} \Vert{Y-XDB}\Vert_{2}$ where $X,Y$ are given matrices. The constraint is the following ...
2
votes
0answers
85 views

Once and for all: Which FEM plattform should I use for a very large multiphysics simulation?

I'm fooling around with the decision on how to build a multiphysics simulation for too long now (also several questions in this forum). First, I thought it would be possible/necessary to write most of ...
1
vote
1answer
46 views

How to set the temperature at the vertices points for a rectangular domain?

Suppose I have to solve the 2-D heat equation in a rectangular domain using the finite difference method, for the boundary conditions say: $T_1$ is the temperature of the right side of the rectangle, ...
0
votes
0answers
15 views

How to make objective elastic SPH model?

I have implemented a constitutive equation of elastic materials (Hooke's law) in my 3D weakly compressible SPH solver based on [1]. The coding seems to be correct. To verify the implementation I ...
0
votes
0answers
36 views

Pivoting in Crout algorithm

Consider the following code, found on wikipedia, that implements the Crout decomposition algorithm: ...
4
votes
0answers
36 views

Lie Expansion Integration V/S Runge-Kutta Schemes

It is known that one can perform numerical integration of particular order by considering the Lie Expansion (http://adsabs.harvard.edu/full/1984A%26A...132..203H). For example \begin{equation} ...
1
vote
0answers
32 views

Issues with self-consistent Poisson-Schrodinger solver

I'm currently in the process of writing a self-consistent Schrodinger-Poisson solver for a device heterstructure (High Mobility Electron Transistor). The algorithm is based off of this journal(1). I ...
3
votes
0answers
46 views

What are some important pros and contras considering using Trilinos?

I'm currently developing a large simulation that will run on many nodes, and, as far as possible, on GPUs. I'm now considering to build it using libraries from the Trilinos project. I would for sure ...
0
votes
1answer
47 views

Numerical method for solving a system with positive definite blocks

I have a system with below coefficient matrix $$ C = \begin{pmatrix} A & B^T \\ B & D \end{pmatrix},$$ where, $A$ and $D$ are square and positive definite. Furthermore, if $B$ be square, ...
0
votes
0answers
49 views

How do I solve Laplace's equation in 2D using spectral methods?

I want to solve the 2D Laplace's equation: $$ \frac{\partial^2 T}{\partial x^2 } + \frac{\partial^2 T}{\partial y^2 } = 0 $$ with boundary conditions: T(x=0)=T(x=1)=T(y=1)=0 and T(y=0)=1 on a ...
0
votes
1answer
35 views

FEM, Direct Stiffness Method with a nonlinear displacement constraint in one node

i have a question about a FE problem im working on. I made a finite element model of an linear elastic block of material (double striped block) attached with a rigid connection to the environment ...
0
votes
0answers
20 views

Could the non-separable data become more separable by using any method of feature selection, extraction or transfomatio, or it's just a waste of time?

Could these meteorological dataset (in the figure below) be separable by any means of feature extraction, transformation, or it would be just a waste of time to make the three classes separable if ...
1
vote
0answers
31 views

How to make the following data separable for the classification into three classes?

The figure below shows the PCA projections of inputs which are 14 meteorological features, (i.e. wind, temperature, humidity, pressure, and so on.) I would like to use any technique to make it more ...
0
votes
1answer
42 views

text file manipulation in MATLAB

I have a text file which contain a combination of string and numbers. for example like following: *Preprint, echo=NO, model=NO, history=NO, contact=NO *Element, type=S4R 1, 1, 9, 189, 84 2, ...
0
votes
0answers
20 views

PML setting goes wrong in COMSOL multiphysics [on hold]

I am working on a nano-optics case using COMSOL multiphysics 4.2a, My model includes a (450nm)(450nm)(450nm) computation domain Unit amplitude EM Plane wave: $e^{-2\pi i n y/\lambda}$ is sent into ...
0
votes
0answers
18 views

Second and Higher Order Order Corrector in Spectral Deferred Correction

I am trying to work out a second order or higher order correction for the method of Spectral deferred Correction (SDC). Specifically using as a corrector a second order or third order multi-step. In ...
3
votes
2answers
126 views

A numerical GMRES example

I'm having trouble understanding how GMRES works. I've read the part in Saad's book and a few others but still I am confused. Can someone provide me a numerical example to understand it better? Or if ...
1
vote
2answers
76 views

How do you generate data for VTK?

I'm currently developing a simulation and I intend to use VTK for visualisation. Furthermore, I fell a bit stupid right now, as I do not find a good example on how to generate the data for VTK. There ...
1
vote
0answers
21 views

How come the use of delay differential equations in model parameter estimation better than ordinary differential equations? [closed]

in systems biology why is the use of delay differential equations better than ordinary differential equations i.e. compartment models in delay modelling? is there a data independence angle in models ...
0
votes
1answer
30 views

amplitude at exact frequency in wide band signal

Could anyone suggest the most computationaly efficient method for finding amplitude of exact frequency having a noisy wide band signal. To be more specific about a task. I have some physical ...
0
votes
0answers
13 views

How can I calculate some properties using Gaussian 09 [closed]

I need to calculate the following properties for a molecule: 1-most negative atomic partial charge in molecule 2-most positive partial charge on a hydrogen atom 3-molecular van der Waals volume ...
-1
votes
2answers
66 views

Stability of matrix equations in MATLAB

Is there a method to check for unconditional stability or positive-definiteness of large matrices in MATLAB? For example, I know that matrices with property M (positive main diagonal elements and ...
2
votes
2answers
51 views

Fitting rectangle to segments in image

I have the task to fit a rotated rectangle of known size into an image like This is a synthetic test case, in the real application, everything is rather blurred. The rectangle has to cover as much ...
0
votes
1answer
116 views

Three body problem in C++

I am in a begginers programming course and we got a little project. I chose to simulate the three body problem using the Euler method. Even though the system is chaotic there are some special cases ...
4
votes
0answers
64 views

Role of the numerical flux in DG-FEM

I am learning the theory behind DG-FEM methods using the Hesthaven/Warburton book and I am a bit confused about the role of the 'numerical flux.' I apologize if this is a basic question, but I have ...
2
votes
0answers
42 views

Clustering similar words and mapping to numbers in Python

I'm familiar with kmeans to cluster data points, but not text.. So I have one column of words in cvs format, which I want to cluster those which have similar word or more, and then mapping those ...
0
votes
0answers
39 views

Can TETGEN generate triangulation of a 2D point set?

I would like to link my Fortran 90 application to a library which would give me Delaunay triangulation (for a 2D set of points) and tetrahedralization (for a 3D set of points). As suggested in Fastest ...
0
votes
0answers
40 views

Optimizing Prices with Julia & JuMP [closed]

I'm working on an optimization program (very new to optimization & Julia), and have a toy problem where I'm trying to optimize product prices based on the product price and cross-price elasticity. ...
0
votes
1answer
50 views

Solving coupled differential equations with multiple independent variables

I am currently using the wrapper odeintw for scipy.integrate.odeint to solve my equations since they are complex-valued. At the moment, I have 3 coupled first-order differential equations with 2 ...
0
votes
0answers
33 views

How to load simple text file with float number matrix / table into Scilab [migrated]

MATLAB and Octave use load and transfer the contents into a matrix variable with the same name. The Scilab load command does not do the same. Also loadmatfile does something different. On some ...
4
votes
1answer
37 views

Recovering pressure from velocity or streamfunction fields

I am interested in 2D channel flow of an incompressible Stokes fluid (Re = 0), with periodic boundary conditions in the x-direction and no-slip at the walls in the y-direction. I have existing code ...
1
vote
0answers
49 views

Generalized Hermite Function as eigenfunction of a differential operator

I'm going through this paper. The article defines function function $\phi_n^\mu(x)$ that is orthonormal on $L^2$ with measure $dm = dx$: \begin{equation} \phi^\mu_n ...
1
vote
0answers
68 views

Solving a large system of nonlinear equations, where timeseries are the unknown

I am trying to solve a problem, which I find quite hard, like, headache-hard. I have to solve the following set of $M$ nonlinear equations: $$F(X)=\begin{bmatrix}f_1 (X)\\f_2 (X)\\...\\f_M (X)\\ ...
6
votes
0answers
55 views

Tucker factorisation to compare multiple PCA decompositions?

This is an entry level question for multiway matrix decompositions. I have a set/population $k$ of entities (here biological cells) for each of which I also have a number ($l$) of flavours of length ...
1
vote
1answer
47 views

Solving linear system $Ax=b$ with Hessenberg matrix using lapack

I need to solve a linear system of the form $$Ax = b$$ where $A$ is upper Hessenberg matrix with the lower bandwidth equal to 1, $b$ is the RHS vector and $x$ is the solution vector. I have a C++ ...
0
votes
0answers
53 views

How does google automatically create 3D cityscapes? [migrated]

In the last years, Google models not only are major cities, but also suburban and rural areas (google video) I read that there are some tridimensional model building algorithm here. How could such ...
0
votes
0answers
29 views

domain decomposition for SPH / particle methods

What are some of the best domain decomposition algorithms for SPH / other particle methods (not purely Lagrangian, e.g., SPH, where particle connectivity associates), in terms of efficiency, ...
1
vote
2answers
76 views

What kind of optimisation algorithm is suitable for a computationally expensive function?

I have a reference value $R$ and a modelled value $M$. $M$ is generated using a stochastic algorithm with parameters $a$ and $b$. The objective is to tune $a$ and $b$ so that $M$ is as close as $R$ ...
5
votes
1answer
102 views

Solve for $C$ such that $C^{T}AC$ is banded of given width

Given a symmetric matrix $A$, the Lanczos algorithm outputs $C$ such that $C^{T}AC$ is tridiagonal. Is there a generalization of this such that $C^{T}AC$ is banded of specific width $w$? Note that ...
2
votes
0answers
112 views

Compute sparsity pattern of matrix product (special cases) [duplicate]

Suppose we have a sparse matrix $A$. If I need the sparsity pattern of $A^2$, is it best to just compute the sparse product $A*A$? I do not actually need to know what exactly the nonzero value are. ...
0
votes
0answers
41 views

What does a negative time stepping mean? (Adaptive time stepping)

Summary behind the problem: The following code aims at solving a static elasto-plastic problem. Like a 2D square mesh based on an elasto-plastic constitutive model like Von-Mises or Drucker-Prager ...
5
votes
3answers
147 views

Constructing random divergence-free velocity fields

I am trying to simulate decaying homogeneous isotropic turbulence. As initial condition I want a divergence-free vector-field, i.e, $\mathrm{div} U = 0$. How do I initialize random velocity field in ...
1
vote
0answers
20 views

Can I exploit symmetry in a two-sided matrix product A*S*transp(A) to gain execution speed?

Let $A$ and $S$ be $n \times n$ matrices. Only $S$ is symmetric. What is the fastest algorithm to compute $S := A S A^T$?
0
votes
0answers
34 views

Oriented object programming in octave

What is the workflow for creating a new class of objects in octave? Say a class named "dynamic_structure" with two properties "period" and "damping" and one method "Free vibration".
6
votes
1answer
76 views

Where does the floating point error come from? (Finite difference using matrix multiplication versus shifts and adding.)

In Julia it appears that one picks up some error terms when doing finite differences using matrix multiplication versus shifts and addition. ...
1
vote
0answers
30 views

Coupled system of differential equations with eigenvalue

I have the following system of coupled differential equations (the Bogoliubov-de Gennes equations for a certain geometry): $$ \begin{cases} -\frac{1}{2}u''(r) + \big[\frac{1}{2r^2} + f_1(r)\big]u(r) ...

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