All Questions

I've got a matrix K, with dimensions $(n, n)$ where each element is computed using the following equation: $$K_{i, j} = \exp(-\alpha t_i^2 -\gamma(t_i - t_j)^2 - \...

To check the stability of my non-linear equations during solving (using Newton's method), I try to calculate the eigenvalues of the generated jacobian matrix. For that I use Arpack. Now, for testing ...

Is there any online implementation for the coppersmith matrix multiplication I have searched alot but can not find any? and if there is not any why is that Isn't this algotithm much faster than ...

Suppose I have a 3d triangular mesh with the topology of a finite cylinder. Let $C$ be a vertex on that mesh. How can I find the shortest path from $C$ to itself that goes around the cylinder? By ...

I developed a Fortran subroutine that allocates memory for the values vector "A" regarding CSR data structure. It also allocates and creates the "JA" and "IA" vectors. However, its taking too long. ...

I am trying to solve numerically the following second order linear ODE: $a \frac{\partial^2 u}{\partial x^2} + \frac{\partial u}{\partial x} \frac{\partial a}{\partial x} + b u =0$, on the domain $[...

So I just picked up a project that is written in fortran90. I am used to coding in python and C. What is really troubling for me is the use of subroutines in fortran90. In fortran people use ...

Documentation in scipy.interpolate (found at https://docs.scipy.org/doc/scipy/reference/tutorial/interpolate.html) states: "The parameter variable is given with the keyword argument, u, which ...

I am not sure whether this question belongs here, but I would like to give it a try and benefit from the experience of the people at scicomp.SE. From my experience, the software quality in ...

I'm reading an article regarding approximating sums using KD-trees (similar to FMM). As part of the effort I'm trying to make sense of this article , which is cited. I'm having trouble understanding ...

I am trying to visualize the time dependence of a free particle given an initial wave-function using Python and I just wanted to know if I could use the in built FFT implementation from NumPy to find ...

I have searched and what I understood was that they use the naive one with several memory and cache optimization but I wanted to know are they using strassen or copper smith algorithms and if they ...

Does Lapack have a routine that, given symmetric $A=A^T$ and $B$, computes the symmetric matrix $B^{-1}AB^{-T}$ (while preserving symmetry exactly)? It would be enough to have this routine for ...

In our university some Ph.D students for computational methods prefer FORTRAN over MATLAB. I can't understand why? What is the difference between them when are used in computational methods like ...

Is there a Fortran subroutine which performs linear interpolation in one-dimenional data? I need something similar to MATLAB function interp1.

I am a novice at PETSC, and I have been trying to write an FVM code for steady heat conduction in 2D using PETSC (square, regular grid, Dirichlet boundaries) Since the large matrix , say A, will be ...

Circuit simulation software based on SPICE (such as ngspice) uses Newton-Raphson method to solve non-linear system of equations ...

Is it possible to view the data stored in the various PETSc data types from within totalview? Ordinarily, PETSc types are integers which act as pointers to the actual data (obviously my understanding ...

I am new to Fenics and just started reading the tutorial Solving PDEs in Python. For simplicity, we can refer to simplest example, page 17 (the linear poisson equation), despite not necessary. My ...

Assume I have a linear system of $A x = b$ which I want to solve with Jacobi iteration. Matrix $A$ is given in CSR format. The vectors are dense. The code for Jacobi iteration is quite clear and can ...

This might be a silly quesntion but recently I've been trying to program the eigenface algorithm using PCA, so I arranged the face vectors vertically in a matrix X such as: X = [x1,x2,x3,...,xn]; In ...

I am using an existing GCC C++ x86 Qt application that filters, displays and stores results computed by some C code. Since the computation by now got too complex for CPUs I intend to port the small C ...

C++ has had the std::valarray class since the C++98 standard. It is meant to facilitate numerical computations, providing the sort of operations one would expect of ...

Suppose $A,B\succeq0$ and $C\in\mathbb R^{n\times n}$. I am hoping to solve an instance of the following optimization problem: $$ \min_{\textrm{permutation matrices }P} \mathrm{tr}(BP^\top AP+C^\top ...

I found this image on wikipedia referring to Barabasi's work on Network Controllability. I tried to verify it. We have a A matrix of dimensions (20 by 20) made as the image suggests. According to the '...

Hey everyone I have a paper that has a method for computing rise and set times of a satellite given a closed form solution. It is a complicated sinusoidal function and the paper has a method to ...

In the context of Monte Carlo simulations, I am trying to learn how I should ensure that the configurations of my system are not correlated for the chosen interval of measurements. I have found out ...

So template matching using correlation is available in a lot of computational packages; OpenCV matchTemplate(), scipy.signal.correlate2d(), IPP CrossCorrNorm, etc. But they all either evaluate ...

I am currently reading the paper PALMPRINT IDENTIFICATION BY FOURIER TRANSFORM by WENXIN LI, DAVID ZHANG and ZHUOQUN XU about identifying persons based on an image of their palm, one version of the ...

Note, there is already a question here, however the answers don't answer the original question, let alone specific considerations when dealing with nearly in-compressible fluids (water). Another ...

I have a time dependent data set where each frame corresponds to a certain date. I need to show the time annotation, much like what Annotate Time Filter does, but show the date instead of time as a ...

I currently need to solve numerically the following reaction-diffusion equation: $$\partial_tu=\partial^2_xu+u-u^2$$ For this purpose, I use the following numerical scheme (Crank-Nicolson??): $$ \...

My question might seem a bit simple. I am trying to solve a system of ODEs using Runge-Kutta method. I am having difficulty breaking down the equations into a system of first order ones required ...

Only the first two sections of this long question are essential. The others are just for illustration. Background Advanced quadratures such as higher-degree composite Newton–Cotes, Gauß–Legendre, ...

Heavily edited question after I realised partly what the problem was I have programmed a simple 2D square finite element solution to the Poisson equation $-\Delta u = f$ The source function ...

Apologies for the terrible title. I'm trying to perform a 10^6 timestep electrostatic particle-in-cell simulation on a rather large mesh, with very limited computational resources (a single GPU). ...

With some given $s$ value, let \begin{equation} \begin{aligned} h(\beta)&=\min(\sum_{i=1}^n(Y_i - X_i\beta)^2, s)\\ &=\sum_{i=1}^n(Y_i - X_i\beta)^2-\max(0, \sum_{i=1}^n(Y_i - X_i\beta)...

Theoretic part From the theory, in Electrostatics inside a real dielectric material between real conductors, in a simple 1D plane geometry between points $P1$ and $P2$, according to the current ...

I am trying to obtain the spatial representation of $u(x)$ (e.g. velocity) from its energy spectrum $E(k)=k^4\exp(-(k/k_0)^2)$, which is given in the frequency domain, provided $|u(k)|=\sqrt{2E(k)}$. ...

I have the following non-linear diffusion equation, for $\ z(x,t)$: $\ z_t = -C(\sin(\omega t))^m x^{hm}(hm x^{-1}(z_x)^n + n z_{xx} (z_x)^{n-1}) $ Any advice for numerical (or analytical) solutions?...

Can anyone see a way to solve this equation efficiently? $$AXB + X\odot C = D$$ I tried a straightforward solution that involved vectorizing $X$ but that turned out too expensive for my application -...

This is part of the code in matlab for a random-walk simulation. To test the code, I'm using steps=[30]; there will be more values, but I want to run it for 1 trial to decrease code processing. <...

Given a $k$-order polynomial in two variable $p(x, y)$ defined on a polygon domain $K$. And I want to numerically expand it to the following form $$ p(x, y) = c_0 + c_1 x + c_2 y + c_3 x^2 + c_4 xy + ...

I have a set of data data.txt which can be fit to a Gaussian function, f(x). I want to determine the coordinates of the point of ...

Where can I find the manual for software library Libxc for exchange-correlation functionals? Links with domain www.tddft.org don't work.

Suppose I have the system: $$\dot{x} = Ax+Bu\\ y=Cx+Du$$ and the following Hamiltonian matrix: $$H=\begin{pmatrix} A & \frac{1}{2}B^TB\\ -CC^T&-A \end{pmatrix}$$ I want to find the ...

I was curious if anyone could help or provide a reference for the proof to the following lemma Lemma: Let $P_{1}$ be the set of polynomials of the first degree and let $W = w(x) : w \in C([0,1]), ...

I'm working with the tight-binding model, and I'm trying to learn the basics of how to compute the Density of States (DOS) $N(E)$ numerically. The DOS is given by $$N(E) = \frac{1}{N}\sum_k \delta(...

I have been looking at an interesting book "Pharmacokinetic-Pharmacodynamic Modeling and Simulation" by Peter Bonate on pharmacokinetic models: the models of how medical drugs work their way through ...

I am trying to implement Poisson image blending as in the paper Poisson Image Editing. This is the task of filling in a masked region of an image by minimizing $$\min_f\int_\Omega \left | \nabla f - \...