# All Questions

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### Batch script for multiple files

I have multiple ascii files like Total-0100.dat and want to batch process using an executable in another directory. In short, 1. I have multiple files with incremnet of 100 or 1000 e.g. ...
5 views

### Evolving nonlinear Schrodinger equation with higher-order algorithms?

First I will give the relevant information for my question, and then I'll ask the question. $\large{\textrm{Background}}$ For evolving the nonlinear Schrodinger equation (NLS), one typically uses ...
22 views

### Very long running time for Haase and Muller (2014) coded in Python + Gurobi

I have read the paper of Haase and Muller (2014) where they present the linear reformulations of the multinomial logit choice probabilities and compare different approaches. I have tried for an ...
56 views

### Increasing the accuracy of numerical discretization

In order to numerically solve the following differential equation: \text{Fr}\{f\} := v(k)\dfrac{\partial f(z,k)}{\partial z} - F(z) \dfrac{\partial f(z,k)}{\partial k} = ...
49 views

### Beowulf Cluster For MD simulations

What would you recommend as an all-in-one cluster management software for a Beowulf cluster? We have about 7(most of them are 8 core machines and 1 is a 48 core machine) very good compute nodes in our ...
79 views

### C++ libraries for Fast Fourier Transform in high precision

I am looking for a C++ library for Fast Fourier Transform (FFT) in high precision (e.g., using high precision real data types similar to mpfr_t in MPFR or ...
94 views

### Fitting with a linear combination of exponentials

I want to elaborate on a statement I read in Acton's "Numerical methods that work", paragraph "Exponential fitting", page 252. Computationally we are being asked to fit only the parameters $A$ and ...
32 views

### Solving Schrodinger's Equation Numerically in a Bunimovich Stadium

I need to solve, as mentioned, Schrodinger's equation in a Bunimovich stadium-shaped infinite potential well with Dirichlet BC Numerically (this isn't possible analytically). In order to do so, I need ...
35 views

### what is procedure for crank Nicolson method in nonlinear partial differential equations? [on hold]

can u tell me step by step of what is procedure for crank Nicolson method to apply in nonlinear partial differential equations? and how to plot it.
67 views

### MPI+OpenMP Scalability

I have a numerical code which is MPI+OpenMP (hybrid) parallelized and an available computational resource of 32 nodes with 16 cores on each node. The code has been tested for MPI scalability up to 16 ...
40 views

### Repeated 1d minimization with similar parameters (scipy)

I have a function f(x,k1,k2) and I am trying to minimize it over x for different values of ...
6 views

### In Content Based Image Retrieval, what is Skewness of a colour moment?

In Content Based Image Retrieval, what is Skewness of a colour moment? and would we expect it to be better or worse for providing accurate results?
79 views

### Robust smoothers for geometric multigrid

I'm searching for robust smoothers for geometric multigrids. By robust I mean: Effective for high order approximations (say spectral element, spectral Discontinuous Galerkin), Parallel (suitable ...
20 views

### the compiler says cds in resize(cds); is undeclared, Can someone help? [on hold]

//header file /* */ ifndef CDS_STRUCT define CDS_STRUCT include "CD.h" using namespace std; struct CDs { CD** cd_array; int num_cds; int max_cds; }; // CDs* createCDs(string ...
43 views

### Methods of solving non-linear advection-diffusion systems beyond Newton-Raphson?

I'm working on a project where I have two adv-diff coupled domains through their respective source terms (one domain adds mass, the other subtracts mass). For brevity, I'm modeling them in steady ...
15 views

### Finding errors in frequency from a Fast Fourier Transform from Gaussian fitting

I took a FFT of sound in a box generated by a frequency sweep over a range of frequencies, and have an array of frequencies and their corresponding FFT amplitudes. According to models for the ...
34 views

### Fixing a near singular covariance matrix

Given a near singular covariance matrix, the standard method of 'fixing' it seems to be to add a small damping coefficient $c>0$ to the diagonal, which serves to bump all the eigenvalues up by this ...
44 views

### On Boyd et al.'s convergence analysis of ADMM: Why do we need the convexity assumption?

Please refer to Boyd et al.'s convergence analysis of ADMM (Chapter 3 and Appendix A). My question is: Why do we need $f$ and $g$ to be convex? I don't see the need of this assumption. If the ...
23 views

### How to alter the standard deviation algorithm to extract edges

I have developed a programme that currently computes the standard deviation of an Image Histogram. I am trying to alter this algorithm so that it can extract the edges of an image. I have been told I ...
66 views

### Pseudo Code for non linear power function fit needed

I am struggling finding pseudo Code for a non-linear fit of the following function: $y = a\, x^b$ Package NLS in R does perform well, but utilizing external software is not practicable in my program ...
23 views

### Minimization of the sum of convex function and non-linear non convex function

I'm trying to minimize the unconstrained scalar sum of a quadratic convex function (to which a convex optimizer is readily applied) and a non-linear and non-convex function which is differentiable. ...
8 views

### Starting structure for stacking interaction energy calculation

I have a crystal structure (single crystal, pyranone carboxamide derivative) that shows $\pi$-$\pi$ stacking, and I want to do theoretical calculations. I am using Dispersion-correcting potentials ...
17 views

### please help me to convert 2d monte carlo simulation program for grain growth to 3d [on hold]

function plotgrainsizedistribution(Tmcs2,nodespool) global L0 lembda K1 n1 global coord global num_of_row y1=num_of_row; tmcs=sum(Tmcs2); %summing the entire tmcs value for the each grain ...
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### Grouping operator in DBMS (Ɣ) is duplicate impervious. Why? [migrated]

I'm reading Database Systems by Ullman where its mentioned that Ɣ is duplicate impervious. I dont understand why a simple group operation should cause elimination of duplicates. Aliter, ...
38 views

### Most efficient and practical way to avoid calculating inverse matrix?

So I've heard about the LU decomposition applied to avoiding calculating the inverse of a matrix and how it's so much more efficient than the typical inverse calculating functions in numerical ...
25 views

### How to discretize Laplacian near refinement boundary

Given a block structured grid with a refinement factor of two, what are some of the common ways to discretize a Laplacian near a refinement boundary? See also the picture below, in which $u_H$ and ...
14 views

### The alternative to using PETSc's SNES solvers in parallel without using the DMDA methods

I am using the PETSc libraries, in particular using the SNES solver package to solve a nonlinear matrix equation. Is there a way of parallelising the solution to this problem problem without using ...
31 views

### Numerical computation of the complex elliptic integral $E(k)$ for medium $|k|$

I have implemented Carlson's algorithm for $E(k)$ from Numerical computation of real or complex elliptic integrals (available from ArXiv eprint, see also DLMF). It is essentially his formula (46) ...
12 views

### PETSC Makefile dependencies and Netcdf

I have built an interface to PETSC for my main code, contained in coreSolver.cpp so that I can use non-petsc data structures and call PETSC when necessary ...
40 views

### Stokes Equation in “two-fold saddle point” form?

Are there papers that deal with the (nondimensionalized) Stokes equation for incompressible fluid flow in a "doubly mixed" form like the following? \begin{align*} 0&=\underline{\epsilon} + ...
53 views

### Divide and conquer for optimizing weakly unimodal continuous function?

Is there a divide and conquer algorithm for optimizing weakly unimodal continuous functions? Adding more details: My function has a flat line on the left and right and then there is a global ...
22 views

### Will Golden Section Search work for optimizing weakly unimodal functions?

Will Golden Section Search work for optimizing weakly unimodal functions? If not is there any variation of it that will allow for optimizing weakly unimodal functions instead of strictly unimodal ...
37 views

### Function similar to erf that is fast at scale and allows for changing the slope at 0?

I'm interested in a function that would allow me to weight my system similar to using the error function; however computing the error function at scale would be a bottleneck. Is there something like ...
352 views

### ODEs vs DAE vs ADE?

I am totally confused between ODEs which I am familiar with, and differential algebraic equations (DAE) and Algebraic Differential Equations (ADE). Are they the same but just different names or what ...