# All Questions

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### Treatment of Neumann (Traction) boundary conditions using projection methods

I am looking to solve the incompressible Navier-Stokes equations in 3D, using an inflow boundary condition specifying a velocity: $\mathbf{u} = \mathbf{g}_0 \,\, \forall \,\, \mathbf{x} \in \Gamma_u$ ...
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### Testing 1D root-finding procedures for robustness

How can I test whether a given 1D root-finding procedure is robust? I know that there are data sets and resources online for different kinds of optimization, but I have yet to find anything with ...
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### How to use the Freefem++ (or Fencis) for solving 3D Helmholtz equations or Maxwell equations

I recently want to solve the three-dimensional Helmholtz equations with ABCs via the edge element method. But I am familiar with the program of C++/Python (-type) language, so I want to obtain some ...
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### Nonsmooth dynamic systems simultion using Siconos sofware with Rhenoumous Rheonomous relations [on hold]

I have been working on a nonsmooth dynamic system recently with Siconos software. However, I think I have encountered some problems and I can not find any solutions. My system can be formulated as ...
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### 3D Poisson equation, Fourier and Chebyshev

I am currently trying to solve the 3D Poisson equation with a Chebyshev discretisation in the $z$ direction (from -1 to 1) and Fourier in the $x$ and $y$ (from $-\pi$ to $\pi$) I have taken the code ...
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### How to determine the number of c points in algebraic multi grid

I am trying to write an algebraic multi-grid solver (in c++). At a given level I determine which nodes are c-points and which nodes are f-points (where the total number of c and f points equals the ...
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### How to generate a rotated (by 90 degrees) logistic sigmoid function in Python

I created this Python function to generate a sigmoid function where I can modify position and width: ...
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### Policies Relating to Publication and Open Source Development of Code in Academia

Introduction Let me first state some conflicting assertions of the matter to illustrate what are the issues. Personally I would like to have my code open at every stage of development, since ...
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### How to use Freefem++ to implement the approximation under the unfitted FE, based on Nitsche's method, for elliptic interface problem? [on hold]

I want to know how to use Freefem++ to implement the approximation under the idea shown in Hansbo's paper. I write down here the main idea, please see more on the paper if you want to see more ...
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### Should I pass command line arguments to MPI_Init or not?

When writing MPI 3.0 code, should I pass argc and argv to the MPI_Init call or not, and why? ...
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### ice (sleet, glaze ice) [on hold]

Tell me how you can well predict the ice (sleet, glaze ice)? I have a database for a long period of time with different parameters to weather conditions. The first thing that comes to mind - Least ...
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### Is there a relatively simple way to extract the Jacobian from a Runge-Kutta 4/5 integrator?

I have a RKF45 numerical integrator that simulates polymerization of proteins using CUDA. It does so by tracking the populations of discrete length polymers, e.g. monomers, dimers, trimers, etc. all ...
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### I can't store my data [on hold]

I use the cluster in my laboratory to simulate something with matlab.And I open many programs at same time.It usually needs about 2 to 3 days to finish the simulation.However,the data of some programs ...
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### Does it matter if I use principal component analysis on the transpose instead of the original matrix?

My data set is a 60x10 matrix. I performed principal component analysis of this matrix with matlab using the princomp(AdjustedData) after I adjusting my original data set by subtracting the mean of ...
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### Boundary conditions Chebyshev differentiation

I was wondering if anyone has any experience dealing with boundaries when implementing chebyshev differentiation. I am currently trying to implement a no slip boundary condition to solve the ...
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### Is the shooting method the only general numerical method for solving nonlinear boundary value ODEs?

During my wandering in Mathematica.se, I gradually noticed that a certain kind of differential equation solving problem is "troubling" us all the time, that is, the boundary value problem (BVP) of ...
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### Implementation of nonlinear term in FEM

Although there are similar questions, I am also struggling with the implementation of the following term in "my own code" by Finite Element Method, namely, $\nabla \phi \cdot \nabla \phi$. $\phi$ is ...
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### General question about Computational Science

I'm student of computer science (BS) and considering computational science as the field to major in for MS program. I have two questions which might look silly but I'm really confused: 1- Are ...
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### What is the smallest positive integer that is not exactly representable as a floating point number in this system?

I have difficulties answering Exercise 3.10 from the book Overton M. Numerical computing with IEEE floating point arithmetic, 2nd edition. What is the smallest positive integer that is not exactly ...
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### Confusion in modeling and computing [on hold]

I come from a computer graphics background without any professional in computational science. But I find my job(game engine development) being related to this field. May I ask some general questions ...
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### optimising changing the range of integers from random number generation

I'm looking to find the most efficient way to change integers from a random number generator to a different inclusive number range. I know of 2 ways so far: Change the number into a decimal in the ...
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### Numerically solve a PDE in Python with a term calculated by coarse-graining

I'm trying to solve a PDE in Python of the form, $\dfrac{\partial c(\mathbf{x}, t)}{\partial t} = \mathrm{D} \nabla^2 c(\mathbf{x}, t) -\gamma \rho(\mathbf{x}, t) c(\mathbf{x}, t)$ where $c$ ...
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### Schur(QZ) Decomposition Differences

I am having issues understanding why different languages are producing different answers for the Schur(QZ) decomposition. I am working on writing some old stuff from Matlab into Julia and Python and ...