0
votes
0answers
3 views

Will future Operational Systems adopt cyclic trees for directory organisation?

The directory structure in current file systems consists of directed acyclic trees of folders were subordinate directories can belong to only one parent directory. This poses radical limitations to ...
-1
votes
0answers
5 views

Octave is telling me I have undefined constants, confused why code isn't working

his should be a really simple little piece of code and yet somehow it isn't running in octave, any help at all will be greatly appreciated! Here is my code: t=pi/2; i=sqrt(-1); ...
-2
votes
0answers
30 views

Fortran95 for IOS/android [on hold]

i am a engineer working for offshore oil/gas field, and i am good with fortran 95. i have written few programs in f95 specific for my work, which i feel would be great if they worked on my ...
-1
votes
0answers
21 views

Big data analysis project ideas? [on hold]

I recently renovated a desktop that had been in storage for a while, and I'd like to put it to use analyzing some big data sets or testing some algorithms or something. Does anyone have any ...
2
votes
0answers
37 views

Does there exist a Fourier transform algorithm for perturbed data?

Assuming I have a length-$n$ real vector $x$ and have already computed its Fourier transform $\hat x$ (in time $O(n\log n)$), I would like to compute the Fourier transform of $y = x + \delta x$, where ...
1
vote
0answers
36 views

Convert an integer to binary using base 2

Given $A$, an array, $i$, the array index, $A[i] \in \{1,0\}$, $M=\sum_i(A[i] * b^i)$, where $b= 2$ I need a function, which given an integer $N$ returns the array representing such number. ...
0
votes
1answer
56 views

How can I generate 3D unstructured mesh on MATLAB

I have been looking to do a 3D mesh for a shallow tunnel FE analysis. The output of mesh node orientation along the element should be counter clock wise direction. How and which material helps me best ...
1
vote
0answers
49 views

FEniCS: boundary conditions with explicit timestepping

I'm trying to implement RK4 scheme in elastic wave equation - stress-velocity formulation. I've extracted assembled matrix and went to the time loop, but the initial condition does not propagate at ...
3
votes
1answer
49 views

Understanding the conditions for which ADMM can be applied

While reading Boyd's paper on ADMM I encountered an issue. Consider the following problem: Problem. Minimize $f(u) + g(v)$ subject to $Au + Bv = c$, where $f$ and $g$ are closed, proper, convex and ...
3
votes
0answers
63 views

Symplectic integration of PDE

I consider ordinary wave equation $$ u_{tt} - u_{xx} = 0 $$ with initial conditions $$u(x, 0) = \exp (-2 x^2) \\ u_t(x, 0) = 0 $$ To solve this problem I approximate $u_{xx}$ with 4-th order ...
0
votes
1answer
60 views

Indexing Nested Loops in C

I am having trouble indexing correctly the below statement in C inside a function and then returning it as a pointer. The returning part should not be confusing - hopefully - however the indexing is a ...
0
votes
0answers
25 views

Angle of rotation at a point in a deformed triangle

I have a 2D triangle which deforms with each vertex moving by some small ($\sin(x) \approx \tan(x) \approx x$) displacement vector. The displacement of any point in the triangle is linearly ...
3
votes
0answers
19 views

Solving compressible inviscid Euler equations with shockwaves in polar coordinates

For the past several weeks I was attempting to adapt Lax-Wendroff or some similar scheme for polar coordinates. The process was complicated due to me being unable to find step-by-step derivations of ...
0
votes
0answers
26 views

Adding a new potential term to DL_POLY Classic

I am using DL_POLY Classic to simulate CO2 behavior in upper mantle conditions. I am trying to use a recently new forcefield for this system. In this FF, the potential energy between two atoms in the ...
5
votes
1answer
29 views

Projection on Stiefel manifold after integration step

A few days ago, I asked how constraints like $A^T A = I$ can be implemented if one wishes to integrate differential equations of the form $\dot{A}=f(A,t)$. Kirill was so kind to point out that a ...
0
votes
0answers
23 views

efficient MPI collective non-blocking communication

I am facing a problem with MPI (Fortran). I have a really big matrix at each node and they differ at different nodes. At some point of my calculations, each node needs the matrix from all other nodes, ...
3
votes
1answer
38 views

Fitting a rectangle to a point set

I have an ordered list of (2d-)points that are forming a (not axis aligned) rectangle and I'd like to recover that rectangle. Approximations like a minimal enclosing rectangle can't be used so that ...
1
vote
0answers
43 views

Solving system of equations with zeros on diagonal

I am using finite elements, Newton Raphson technique and MUMPS direct solver, to solve for $P$ in this equation: $$\frac{\delta K}{\delta x} \frac{\delta P}{\delta x}= \frac{\delta K B}{\delta x} + ...
0
votes
0answers
16 views

CPLEX Presolve claims infeasibility while conflict refiner says problem is feasible [on hold]

I have a QP which is claimed to be infeasible by Cplex presolve. But when I run the conflict refiner, I am told that there is no conflict available. Any ideas why this may happen, and how to figure ...
4
votes
0answers
24 views

Pseudoinverse of perturbed matrix

How does the pseudo inverse of a full column rank matrix change if I rescale a single row? In more detail the problem is the following: We have a fixed matrix $V$ with linear independent columns and ...
3
votes
1answer
63 views

Condition number of $X^{T}AX$

$A$ is a symmetric matrix and is known to be invertible. $X$ is rectangular of size $(N+p) \times N$ with $p > 0$ but full column rank. Can we provide an upper bound on the condition number of ...
3
votes
1answer
45 views

Runge Kutta for wave equation

Recently I work on mechanical shocks (e.g. impact) in FE (fenics). I've already put together simple timesteppers (Euler, Crank-Nicolson). I use higher order basis, so I think of higher order time ...
0
votes
0answers
15 views

Markov (Chain) image generators?

Markov Chains can be used to generate, or auto-complete, text. https://en.wikipedia.org/wiki/Markov_chain#Markov_text_generators Training text is read, and some information about the text is ...
-2
votes
0answers
18 views

AI Project went from sluggish to not loading, is it my RAM and or my CPU/processor? [on hold]

I made my Artificial Intelligence program so big that it went from sluggish trying to add blocks to not loading it and now gets stuck at loading screen. And I'v waited like over 15 minutes and if I ...
0
votes
0answers
17 views

How to apply asymptotic matching condition in bvp4c?

I want to know how to write the code to apply asymptotic matching condition? In the paper, it is stated that they apply asymptotic matching condition for the range of ...
3
votes
0answers
12 views

Choosing suitable polynomial degree based on information in advection stencil

I'm working on a finite volume advection scheme for unstructured meshes which uses a multidimensional polynomial weighted least squares fit for interpolating from cell centres onto faces. In 2D, the ...
3
votes
1answer
55 views

Continuous vs discontinuous pressure elements in fluid flow problems

When solving fluid flow problems using finite elements you typically end up requiring that $p\in L^2$. For Darcy flow problems, a popular choice of elements is the Raviart-Thomas element and ...
0
votes
0answers
28 views

Find eigenvalues and eigenvectors using lanczos method [duplicate]

Can anyone help me out for finding eigenvalues and eigen vectors using Lanczos method?
3
votes
0answers
31 views

ADMM for Linear Program over graph

I want to use ADMM to solve a LP defined over a graph. According to Distributed optimization and statistical learning via the alternating direction method of multipliers S. Boyd, N. Parikh, E. ...
0
votes
0answers
47 views

Calculating derivatives

I have this formulation and want to calculate its derivatives using a mathematical software, either Matlab, Mathematica or anything else. Is there any way by which I can obtain the second equation ...
6
votes
1answer
45 views

Approximation properties of FEM projections operators on a boundary

We have an elliptic projection $$P: V \rightarrow V_{h}$$ which satisfies $$\Vert u - Pu \Vert_{L^{2}(\Omega_{e})} \leq Ch^{k+1} \enspace .$$ Can we say anything about $\Vert u - Pu \Vert_{L^{2}( ...
0
votes
0answers
30 views

Constrained SVD/Lanczos given left/right matrices are banded

$A$ is a symmetric (known to be invertible) matrix of size $(N+p) \times (N+p)$ and $X$ is a rectangular matrix of size $(N+p) \times N$. The product $X^{T}AX$ is well-defined and non-singular. One ...
0
votes
0answers
21 views

Sparse Matrix-Matrix Multiplication using SUMMA

I'm a beginner to SpGEMM(General Sparse Matrix-Matrix Multiplication). I want to know how SUMMA(Scalable Universal Matrix Multiplication Algorithm) for sparse matrices works. There are a few papers ...
6
votes
1answer
43 views

Velocity-Stress formulation of Elastodynamics/Wave Equation for beginner

I'm used to displacement forumlation of elastic wave equation: $$ \nabla \cdot \sigma (u) + F = \rho \ddot{ u } $$ where $u$ is the primary variable. Recenty I started experimenting with DG and in ...
0
votes
0answers
38 views

PDE discretization (via finite difference sheme) question

So after posting this question and reading all your comments I would like to make this new question (update). If you consider the three equations presented here: $$\frac{\partial \rho}{\partial t} ...
0
votes
1answer
48 views

How to deal with transition elements in adaptive fem

It is necessary for me to solve a Poisson equation by adaptive finite element method with transition elements technique to get conforming mesh. For the first local refinement everything is OK, ...
1
vote
1answer
33 views

Non-uniform finite difference Adaptive Mesh Refinement

Assuming that the crosses in the figure below are unknowns in a vertex-centered finite difference scheme in an Adaptive Mesh, how can I calculate the double derivate (Laplacian) at the Red x ? The Red ...
0
votes
0answers
17 views

How to cluster words using Jensen-Shannon Divergence?

I'm working on a project that requires text analyzing. I'm currently trying to extract keywords from a single document. I referred to this thesis(Keyword Extraction from a Single Document using Word ...
3
votes
1answer
56 views

Efficient Quadrature Methods for Indicator Functions?

I am looking to numerically solve many different integrals where the integrand is simply the indicator function for a region (i.e. 1 on the region, 0 outside. This is for measuring areas). The ...
10
votes
2answers
83 views

pointwise vs. continuous observations in PDE inverse problem

I work on an inverse problem for my Ph.D. research, which for simplicity's sake we'll say is determining $\beta$ in $L(\beta)u \equiv -\nabla\cdot(k_0e^\beta\nabla u) = f$ from some observations ...
3
votes
1answer
87 views

Integration of differential equation with orthogonality constraint

Lets say I have a system of differential equations which has the form $$\dot{C}_{\alpha,\beta,m} = f_{\alpha,\beta,m}(C_{\alpha,\beta,1},\ldots,C_{\alpha,\beta,N};t).$$ The $f$s are some functions of ...
1
vote
0answers
16 views

How to find active region in treepartition Matlab object

I am trying to identify a non-linear plant using the identification toolbox of Matlab. In particular I would like to identify a non-linear arx model, where the nonlinearities are expressed by means ...
5
votes
1answer
53 views

Proof of CFL condition for RKDG scheme

The cfl condition for linear advection equation $$ u_t + a u_x = 0 $$ using a DG method of degree $k$ polynomials, upwind flux and an RK scheme of $k+1$ stage/accuracy is stated to be ...
-1
votes
1answer
48 views

Solving coupled PDE in COMSOL [closed]

I have the system of equations \begin{align} &A \frac{\partial u_1}{\partial t} = 1 - u_1 B \frac{\partial u_2}{\partial y}\\ &\frac{\partial u_2}{\partial t} = \frac{\partial}{\partial ...
0
votes
0answers
21 views

Entering an Electric field dependent equation in material contents in COMSOL?

I am trying to model a CNTFET in COMSOL. I am following the same steps that were used to model a MOSFET (provided in the semiconductor module manual), except for a few additional layers and materials. ...
1
vote
0answers
44 views

Monte Carlo Metropolis method - trial step algorithm

I'm working on a Magnetization simulation and writing an algorithm using the metropolis method. I am using a change in energy and a Boltzmann distribution, but, my question is about the trial step. ...
3
votes
0answers
22 views

Data analysis of a magnetic hysteresis loop

I am a physics undergrad and I have MOKE data for a magnetic material (thin permalloy film on a silicon substrate). Here is one of the hysteresis loops I obtained, plotted using Python: The form of ...
8
votes
5answers
448 views

Choice of basis in FEM

Briefly, what are the different types of basis used in FEM and why is the nodal basis so popular and advantageous in the finite element context?
2
votes
1answer
47 views

Help understanding and implementing fast multipole method for N-body

I've been trying to understand the Fast Multipole Method but not really getting anywhere. It seems like the fastest mainstream N-body simulation algorithm, and I would like to implement it in an ...
5
votes
1answer
201 views

Does this Algorithm (probably Fourier like) Exist for 2D Shapes? [closed]

Update: Someone changed the title to this post to a possible answer ("Fourier decomposition of parametric shapes") but I changed it to a different title as that makes it clear what I was asking. As I ...

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