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Questions tagged [c++]

A powerful object oriented programming language.

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3
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5answers
1k views

Speed of solving linear system with block diagonal matrix

I have a bunch of 3x3 linear systems of the form $Ax=b$. In general, would it be faster to solve each individual system, or to formulate it as a giant block diagonal system and solve that? I expect ...
0
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1answer
318 views

Debugging in parallel mode using Netbeans

I want to debug a c++ code with Netbeans. I can use the debugger in sequential mode but I dont know how to debug it when I want to run it in parallel. I would be grateful if anyone help me on this ...
0
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2answers
1k views

Simulating a traveling sine wave

I'm trying to make an animation of a travelling sine wave (amplitude vs. position) would anyon here happen to know how to do so?
3
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1answer
246 views

non-smooth convex c++ solver

I happened to know that there are advanced established techniques for non-smooth convex optimization in research. For example, these two papers: Nesterov, "Smooth minimization of non-smooth functions"...
1
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1answer
817 views

How can I call the Boost C++ odeint Runge-Kutta integrator for a system of ODEs?

I would like to use Boost C++ odeint Runge-Kutta integrator on a system that looks like this : $$\ddot x = - \frac A{||x||^3} * x $$ $ x $ is a vector in 3D space, so basicaly $ x(i, j, k) $ $ \...
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1answer
293 views

Solving electron density function for Hydrogen and drawing in 3D

I recently stumbled upon interesting site that has interactive 3D representation of radial electron distribution (atomic orbital). here is the url: http://winter.group.shef.ac.uk/orbitron/AOs/1s/e-...
3
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1answer
333 views

Computing the (non-convex) boundary of a set of paths between two points

I have a set of paths between two fixed points (marked in red below). Each of these paths consists of an ordered series of $\{x, y\}$ points (marked in blue). I am trying to find the ordered set of ...
6
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2answers
6k views

Programming Finite Element Methods in C++

I am trying to develop a library for finite element methods in C++ and for that I am looking at the data structures for meshes. Based on what I've read up on fenics and deal.ii, the general ...
0
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1answer
987 views

Domain Decomposition with PETSc

Does anyone have any experience on Domain Decomposition using PETSc library? I have used PETSc for creating my vectors and matrix within my C++ code. I also used KSP to solve the linear system. I ...
3
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0answers
902 views

total memory usage of MPI shared memory

I am trying to use the MPI share memory feature. I have several SMP nodes, and each of them has four cores. I need an array of size N for each node that should be accessed by all four cores in each ...
1
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1answer
233 views

Windows C++ library for operations on mesh with a mex-interface in Matlab?

Please recommend me a well documented C++ library that I could wrap with a mex-interface in Matlab. The library should have the capability to read meshes (optimal in different formats, at least in ...
0
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2answers
108 views

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 ...
8
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2answers
5k views

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? ...
0
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1answer
416 views

Fastest linear solver for sparse positive semidefinite, striclty diagonally dominant matrix

What is the state of the art for fastest linear solver for sparse, positive semi definite and strictly diagonally dominant matrix with N varies from ~700 to ~3000, and about a 1/16 of the matrix is ...
0
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1answer
382 views

How can I use Scipy to fit data generated from a C++ model?

I currently have a functioning and blazing fast model written in C++ and CUDA. However, I'd like to use Scipy.minimize to fit the model to some experimental data. I was hoping it would be easy, but ...
5
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2answers
521 views

Machine precision and local error

I'm working with an RKF45 integrator that I have programmed using CUDA C++ on my GPU and am pondering a few questions as I'm trying to track down some issues with my code. I'm using double ...
10
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4answers
2k views

Looking for Runge-Kutta 8th order in C/C++

I would like to use Runge-Kutta 8th order method (89) in a celestial mechanics / astrodynamics application, written in C++, using a Windows machine. Therefore I wonder if anyone knows a good library / ...
0
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2answers
3k views

Most efficient library to diagonalize exactly large hermitian or unitary matrices

I am working on a physics problem which requires obtaining the exact eigenvalues and eigenvectors of Hermitian and Unitary matrices numerically. Naturally I would like to ask the experts what are the ...
1
vote
1answer
481 views

How to minimize the artefact of a cartesian to polar transform followed by a polar to cartesian transform?

I'm transforming cartesian images into polar images. (x,y) => (angle, radius) I fill the polar image by iterating on each of its pixels and filling them by doing the reverse polar transform. For a ...
2
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2answers
241 views

Suggestions for open source C++ library for medium scale non-linear solver

I need to find the root of a nonlinear system (which comes out of collocation, so I will change the order to test). I will likely have about 50-300 variables, and the Jacobian is going to be ...
6
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4answers
4k views

How to efficiently assemble global stiffness matrix in sparse storage format (c++)

I am writing a finite element solver in C++. The main bottle neck is assembling the global stiffness matrix in sparse compressed row storage (so far I am only solving steady problems). Because I don't ...
7
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1answer
137 views

Do C++ matrix libraries translate compound vector operations to single loops?

I am trying to replicate Fortran90 array syntax using a C++ library. The libraries themselves are discussed at length in this question. They can all do something like this: ...
3
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1answer
626 views

Accurate implementation of the logarithm of the incomplete Beta function in C++?

I need an accurate implementation (for use in C/C++) of the logarithm of the incomplete Beta function: $$\log \mathrm{B}(x,y;\alpha,\beta) = \log \int_x^y t^{\alpha-1}(1-t)^{\beta-1}\mathrm{d}t$$ ...
0
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1answer
177 views

GMRES: Making the matrix square without solving for boundaries

How do we define the matrix for GMRES, if we do not want to solve the boundary elements but only the interior ones. I am using pentagonal elements so in a row there are 6 elements (cell itself + 5 ...
2
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1answer
509 views

Not enough memory for GMRES

After realizing that Gauss-Seidel is extremely slow for my simulation, i wanted to try GMRES and luckily found the C++ code here without diving into the theory. The size of the matrix in my case is <...
2
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3answers
377 views

importing PARI libraries ( in C++) with Python

I noticed that Python does not have a good datatype for rational numbers, certainly not for algebraic numbers like $\tfrac{1 + \sqrt{2}}{3}$ or the real root of $x^3 - 5x + 7$. They have the ...
20
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10answers
12k views

Fast, lightweight C++ tensor library for dimension-agnostic code

I am looking for a C++ tensor library that supports dimension-agnostic code. Specifically, I need to perform operations along each dimension (up to 3), e.g. calculating a weighted sum. The dimensions ...
1
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1answer
146 views

what went wrong with my logistic regression implementation in c++?

I have implemented a simple logistic regression function with IRLS algorithm using the armadillo linear algebra libray ...
9
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10answers
4k views

Is it possible to optimise this integration code so that it runs faster?

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1
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1answer
872 views

Coding complex equations into C++

I have here equations from a paper by E. Bradlow. They're for counting the events in a Weibull-distributed data set. $$\begin{align} \Pr(N(t)=n) &= \sum_{j=n}^\infty{\frac{(-1)^{j+n}(\lambda t^c)^...
22
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5answers
5k views

What language should I use when teaching an undergraduate course in computer programming?

Going to teach students of undergraduate level a course titled Introduction to Computer Programming. I am confused a bit. In Computational Physics scientists use C/C++ or Python or Fortran,CUDA etc.......
3
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3answers
1k views

Leave openMP theads ready

I have a C++ program that has a double for loop that I'd like to parallelize using opeMP. It is simple (a polynomial product) of varying length (between 100 and ...
2
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1answer
3k views

How to use TrangularView class in Eigen C++

For a nonsingular lower or upper triangular square matrix $A$, how to solve such linear system in Eigen: $$A x = b$$
1
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1answer
1k views

How can I reuse the SVD of matrix A to solve LS problems for both A and its transpose via Eigen C++?

If $A\in R^{m\times n}, b\in R^m, c\in R^n$, if I need to solve the least square problems via SVD of $A$ and $A^T$, i.e. I need to solve the least square solutions to following linear systems via ...
4
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1answer
225 views

What is the most efficient way to obtain the max eigenvalue of a specific symmetric matrix via Eigen C++

Suppose I have a symmetric matrix $A_{1000\times 1000}$, which can be represented by: $A = J G J^T$ where $J$ in 1000x3 is full column rank dense matrix; $G$ in 3x3 is a nonsingular dense matrix. ...
6
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3answers
6k views

Which algorithm to use for solving an LP with a very large number of variables?

I'm a newbie at modelling and optimization of LPs. My research problem concerns assigning tasks/jobs to virtual machines in a data centre depending on the least energy cost incurred. As you can ...
4
votes
1answer
971 views

Solver suggestion for many small quadratic problem in C++

I have a C++ program/model that in some parts already use IPOPT (with ADOL-C and ColPack) to solve some pretty large non linear problems. Now in an other part of the program I need to solve a large ...
2
votes
1answer
85 views

How can I efficiently position the different segments of a large vector in Eigen C++?

I have a very large(up to 9 000 000) VectorXi vector defined in Eigen C++ which is read from a data file. The vector consists of 0, 1, 2, ...n segments with ...
9
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1answer
616 views

Implementation of Jacobi-Davidson method for cubic eigenvalue problem

I have a large cubic eigenvalue problem: $$\left(\mathbf{A}_0 + \lambda\mathbf{A}_1 + \lambda^2\mathbf{A}_2 + \lambda^3\mathbf{A}_3\right)\mathbf{x} = 0.$$ I could solve this by converting to a ...
2
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1answer
3k views

Implementation of the Numerov Method for the 1D square well

I want to solve the Schrodinger via the Numerov Method but I had some troubles. I'm programing in C++, so here is my code: ...
2
votes
1answer
507 views

How to implement the spectral decomposition of a symmetric dense matrix via Eigen C++

Spectral decomposition of symmetric matrix $A_{n\times n}$, specifically, $n=3$ find the orthogonal matrix $Q$ and diagonal matrix $\Lambda$ such that: $A=Q\Lambda Q^T$ How to implement such ...
3
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2answers
658 views

How to re-use the coefficient matrix decomposition result when solving linear systems by Eigen C++

My problem needs to solve dense symmetric linear systems something like: A x = b, A y = x, ...
2
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1answer
965 views

Particle Tracking Code - MATLAB vs. C++

First some background, I am a mathematician by training with very little formal training in programming. I am most comfortable in MATLAB and have been working with it for a long time. My second choice ...
3
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3answers
3k views

C++ Libraries for solving Complex Linear systems Ax=b [duplicate]

I am interested in solving a sparse complex linear system Ax=b where A is a square matrix of complex numbers and b is vector of complex numbers. If possible I would like such a library to be ...
3
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1answer
3k views

How to change the dimensions of an Eigen Matrix in a loop?

I have a while loop, in which I use a Matrix A, vectors B and x with varying dimensions: <...
3
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2answers
657 views

How to avoid precision loss when handling very long integer constant involved multiple precision computation?

I have a numerical computation problem which requires solving nonlinear equations (with long integers) in multiple precision. I tried an MPFR C++ wrapper from this link by Pavel: mpfr C++ wrapper by ...
4
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2answers
329 views

Can the Levenberg-Marquardt algorithm be used for minimization and not fitting

Can the Levenberg-Marquardt algorithm be used for minimization and not fitting? Usually we input the derivative of the function we want to fit in the minimizer. Now if I assume I have an objective ...
2
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4answers
11k views

What's the simplest way to graph a 2d array generated in C++ using Windows 7?

This was so much easier in Python (so much so that I'm considering going back to matplotlib for data analysis). But really, trying to figure out ROOT and Boost graph library and mathgl makes me want ...
8
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1answer
1k views

Why am I getting so much error for my Runge Kutta Fehlberg solver?

My current project is a reprogramming of a protein folding model involving the solution of thousands of ODEs in C++. I've been making some stop and start progress as I'm writing the solver to run ...
3
votes
2answers
1k views

How Do I solve large systems given UMFPACK memory limitations?

I am trying to solve a system of equations (A x = b) for 3D heat diffusion (i.e. each equation has at most 7 terms not including the constant "b" term) using UMFPACK with boost numeric bindings to C++....