# All Questions

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### Numerically calculating the divergence of a set of oriented points

Say I have a set of oriented points at locations $\vec{v_i}$ with each some direction $\vec{n_i}$, in practice they represent a surface with its normals. How would I calculate the divergence of this ...
11 views

### Why can't I send or receive Yahoo email?

Why can't I send or receive Yahoo email? If you are facing trouble in sending or receiving mails, then you can contact us at Yahoo Customer Service Phone Number . The problem behind this could be very ...
127 views

### In FEM, why is the stiffness matrix positive definite?

In FEM classes, it's usually taken for granted that the stiffness matrix is positive definite, but I just can't understand why. Could anyone give some explanation? For instance, we can consider the ...
27 views

### Second order tensor visualization software

Is there an overview available over tensor visualization software? My personal preference is: A software which is free, well documented, and offers visualization techniques for different physical ...
14 views

### How to construct a subring of a polynomial ring in Magma

This is a question about the computer algebra system Magma. I have been looking for a place to ask this type of question on the SE network and scicomp.SE was suggested to me; hopefully it finds a home ...
20 views

### Algorithm for solving system of quadratic equations and linear equations

Let $x \in R^N$. From a Spectral Chebyshev collocation method, I have a system of quadratic and linear equations. Denote them, $$x^T Q_i x + L_i^T x = 0$$ and $$A x = 0$$ Furthermore, I know ...
35 views

### Are FEM or DGFEM methods based on integrals or PDEs?

I know that FVM is based on the integral form of conservation laws, and FDS is based on PDEs. What I'm confused by, is whether FEM and DGFEM formulations are based on integral or pde form of ...
17 views

### Eigen - store sparse matrix as binary

I need to store large sparse matrices in Eigen. I cannot find anything in the library except the function below, in Eigen/Unsupported. The problem with saveMarket is, that it saves in text format. Due ...
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### Star alignment (algorithm) [on hold]

I'm new here and I need your urgent help. I have to get my homework done. It's about to allign multiple sequences using star algorithm. Does anybody know where can I find flow chart or smthng like ...
56 views

### Total Flop count for LAPACK DPOSV

I am looking at the LAPACK DPOSV routine that computes the solution to the real system of linear equations A * X = B. The routine description can be found here: ...
54 views

### Inverse quadratic method only makes one iteration - python

I'm tryin' to implement this method with python3 but i don't solve the problem. This is my code: ...
52 views

### Projectile motion in non-uniform field [on hold]

I have to model projectile motion in a non-uniform field, using Newton's law of gravity. To calculate motion in the non-uniform field I have been told to use Euler's method. I've been given a class ...
29 views

### FFT-based Image Rotation Algorithms More Accurate Than Chirp-Z?

We're currently using a Chirp-Z based implementation (Tong and Cox, 1999) for rotation of astronomical images. I was wondering if there were any algorithms/implementations out there that could also be ...
22 views

### Detecting label errors using a classifier in scene labeling

I have a classifier for two classes that was trained in a convolutional neural network using cuda-convnet. Input are hand-labeled greyscale images, it is part of a scene-labeling project. What I'm ...
11 views

### dynamic array in c++ [migrated]

I need to do a code by c++ that imolement adynamic array 5*5 every element in it is equal to the sum of it's index for example : first elemnt of index (0,0) it's value is 0+0=0 and so on here is my ...
72 views

### Calculation of error

I have written a code in which I find the approximation of the solution of this elliptic problem. I calculated the error using the following part of code: http://pastebin.com/7b5mmuRW but I get the ...
83 views

### Topics about the deal.II finite element library class “SparsityPattern”

When learning the deal.II FE library, I am a bit confused about the mechanism of its "SparsityPattern" class. Through reading the documentation, I only got to know that it uses the Compressed Row ...
96 views

### What is a “hanging node” in the finite element meshing?

When reading literatures about finite element method, the term "hanging nodes" can often be encountered. Could anyone tell me what indeed is a hanging node? Thanks in advance.
127 views
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### Unrealistic solution for advection-diffusion-reaction PDE with heterogeneous media

About the code: I have a code which simulates concentration from advection-diffusion-reaction PDE in 2D space (X,Y) with time. The solution is obtained using fully implicit finite-difference method ...
60 views

### understanding interior penalty jump of basis function

If cardinal basis functions are used (i.e. $\psi_{ij}=1$ iff $i=j$, and 0 otherwise) in interior penalty methods for elliptic equations such as SIPG & NIPG, shoudn't the jump in basis functions ...
51 views

### Integrating a function and then plotting it's graph in Matlab

I've been working on this code for some hours and it seems I'm doing something wrong which I just can't figure out. I have a function which I integrate and then plot it's values. But the graph I get ...
52 views

### BCs in a coupled problem

Consider a thermo-mechanical coupled problem, where coupling exists from both the sides, mech-loading producing thermal effects and vice-versa. In such a case, is it necessary to always prescribe a ...
16 views

### ufl.log.UFLException: Coefficient and argument shapes do not match! when computing Jacobian in fenics [closed]

Am trying to solve a nonlinear system of couple pdes in Fenics and I got this error when computing the Jacobian. My functions consist of U, u, phi, p, where U and u are vector functions and phi and ...
44 views

### How to separate text from the paper on a black and white page?

I tried to discretize an image into black and white and came into some difficult. The difference between the letters and paper is pretty clear to our eyes: However a simple thresholding trick ...
94 views

### computing turbulent energy spectrum from isotropic turbulence flow field in a box

I have my 3 dimensional velocity flow-field u, v and w at a given instant of time from DNS using pseudo-spectral method. I need to calculate the energy spectrum ( in Fourier space ) as a function of ...
34 views

### How can I obtain the solution of dual problem using YALMIP to solve SDP model [closed]

My model is: My code is: X = sdpvar(N+1,N+1); ops = sdpsettings('solver','sedumi','savesolveroutput',1,'savesolverinput',1); obj = sum(sum(C.*X))+trace(X); Constraint = set(diag(X)==1); ...
31 views

### Could This Be Done? [closed]

Could you make this cartoon a reality if so how could I do this?
65 views

### Time discretization of wave equation

I am trying to model the seismic wave equation and have therefore been reading about discretization schemes and their stability. I recently came across an insightful paper on 'Galerkin FEM methods for ...
210 views

### Does OOP work easily and efficiently in parallel computations? [on hold]

I am working on a task for which the object oriented (OO) approach fits well. I am doing it in MATLAB, since I am in the prototyping phase. However, I know that later I will surely have to perform ...
28 views

### Mapping of infinite domain

I am integrating an ODE. For simplicity let us consider a simple one: $\dot{x} = u$ The solution is simply, $x = ut + x_o$. Now suppose my $x$ goes from 0 to $\infty$. But I want to do the ...
119 views

### Understanding Neumann BC

I understand what Neumann BC means physically and how to imply them. However, I am not able to perfectly understand it the way it is represented mathematically as $\partial u / \partial n$ where $n$ ...