Questions tagged [c++]

A powerful object oriented programming language.

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9
votes
6answers
1k views

Soft Question: Where does Python fit into the picture?

So I've been debating whether or not I should bother learning Python. From speaking with my professors, Matlab seems to be the common language used in applied mathematics/computational science as far ...
7
votes
3answers
3k views

ROOT (CERN C++ Libraries) alternatives

I have been slowly learning C++ and ROOT for over a year now, in order to debug a program made with it. Now I reached a point where I can really understand that this will never become easier. ...
1
vote
1answer
95 views

C++ - Starting paraller instances of an executable from a C++ code

Can I start parallel run of LAMMPS from inside a C++ code. Is it possible to compile my code and then do mpirun with my compiled code. I also have one system command inside the code, which starts ...
20
votes
6answers
3k views

Analyzing Numerical Error in C++ Function

Suppose that I have a function that takes as input several floating-point values (single or double), does some computation, and produces output floating-point values (also single or double). I am ...
9
votes
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 ...
1
vote
1answer
234 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 ...
6
votes
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 ...
2
votes
1answer
368 views

Recommendation for C/C++ library which offers Schur complement functions?

I need to find C/C++ libraries which offer function for computing Schur complement. I know about MUMPS and Pastix, but I need more of them to compare them in my research. Do you have any experience ...
2
votes
1answer
584 views

Interpolation using compactly supported radial basis function

I have been struggling for two days with the following problem. I would like to do a $d$-dimensional interpolation over some data. I tried first to use polyharmonic splines, but when the size of data ...
3
votes
2answers
2k views

C++ Library: What is the common libraries that do polynomial arithmetic?

I need to know what libraries (in C++) support polynomial arithmetic specially over a field. So I can give to it an array of coefficients of polynomial over a field and it returns the roots of ...
2
votes
0answers
95 views

C++: How to find the roots of polynomial modulus N [duplicate]

I need to know what library, given a vector of coefficients and modulus N return the roots of polynomial modulus N. The library should support big integer. I'm coding in C++.
4
votes
3answers
583 views

Minimization of non-linear function

Problem Summary I am trying to estimate the (x,y) coordinates of each node in a graph, where I know the distances between connected nodes. For example Given this ...
11
votes
1answer
6k views

Applying the Runge-Kutta method to second order ODEs

How can I replace the Euler method by Runge-Kutta 4th order to determine the free fall motion in not constant gravitional magnitude (eg. free fall from 10 000 km above ground)? So far I wrote simple ...
0
votes
1answer
69 views

Unexpected behavior, values tend to converge instead of fluctuate. (MD)

I am writing a molecular dynamics program to create an lattice and populate it with atoms/molecules. These then are given random velocities and the system is initialized. Then throughout time the ...
1
vote
2answers
804 views

Parallelization of element-wise matrix multiplication

I use Armadillo as an interface to OpenBLAS. In my current program, I have a loop, in which I do multiplications of the form ...
1
vote
0answers
90 views

Elemental vs DPLASMA

I want to use one of these two libraries into my C++ project to basically invert a dense matrix (with Cholesky). Of course, I am interested in a distributed environment. Both libraries seem nice so ...
8
votes
6answers
10k views

Super C++ optimization of matrix multiplication with Armadillo

I'm using Armadillo to do very intensive matrix multiplications with side lengths $2^n$, where $n$ can be up to 20 or even more. I'm using Armadillo with OpenBLAS for matrix multiplication, which ...
1
vote
0answers
246 views

Memory allocation error with GSL ODE solver applied to system of 4 ODEs

I am trying to solve a (large) system of ODEs with GSL solvers. When I use driver method I get an error message of could not allocate space for gsl_interp_accel, ...
3
votes
1answer
630 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: $$\log \mathrm{B}(x,y;\alpha,\beta) = \log \int_x^y t^{\alpha-1}(1-t)^{\beta-1}\mathrm{d}t$$ ...
8
votes
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? ...
3
votes
1answer
369 views

Software for triangulating a point set (with restrictions)

I want to triangulate a point-set like the one below. I would like the triangulation of the point-set to have the following properties The triangles must have as vertices the black and orange points ...
3
votes
2answers
626 views

Why is SIMD programming on such a low level in CPU's compared to GPU's?

Just speaking from my experience in c++ - Its really tricky to take advantage of the SIMD capabilities of modern CPU's for more complex algorithms. If I see an opportunity from a high level OO ...
3
votes
2answers
624 views

literature on scientific computing

Maybe, this is a dump question. But anyway. I developed a finite difference code for a class of problems in dynamo theory. I used GNU Octave (MATLAB) which is good for testing. The problem size ...
2
votes
1answer
281 views

Mathematica NIntegrate function in C++

I am working on computing a challenging integral. I am working with someone else who wrote some code in Mathematica to compute it. I do not have mathematica so I am trying to do the same thing in C++. ...
0
votes
1answer
1k views

Order of eigenvalue problem using c++ Eigen library

I have the following 6x6 matrix (taken from Google Books p. 129): For background info: All the entries depend on the momentum $k$. Getting the eigenvalues of this matrix for each $k$ corresponds to ...
2
votes
0answers
86 views

Bracket Algebra, Straightening Algorithm

My apologies if the question is simple. I need to write a code for straightening algorithm. Which includes defining bracket algebra. I tried to write it in CoCoA-5, but it wasn't possible because ...
3
votes
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
votes
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?
4
votes
5answers
1k views

Finding the correct Molecular Dynamics library

I just started working on some Biophysics research, and I was looking around for a good MD library to use. There is one right now at the university set up in C, with openMC parallelization, but the ...
1
vote
0answers
403 views

Get a single value from a global Vec in petsc [closed]

I don't understand the concept with local and global vec's in petsc when it come to DMDAVecGetArray and VecGetValues. I'm creating some DMDA Vec in parallel which works well. Now I want to access ...
2
votes
1answer
117 views

What are the tradeoffs of using statically allocated arrays vs. pointers and dynamic allocation? [closed]

I am learning Monte Carlo simulation by C++. I begin with reading codes (from the internet and text books) of the 2D Ising model and the XY model. I find some people define spins simply by a two ...
7
votes
4answers
7k views

How to find more than one root of a polynomial?

This program finds the first root of the function f, defined in the code. There are 5 roots of this function. (x=1,2,3,4,5) I wish to find all of the roots in this program and print them to the screen....
2
votes
1answer
2k views

Parallel vs Serial Thomas Algorithm

I am currently writing a code that solves a large tridiagonal matrix every iteration and runs for 1,000's of iterations. I am currently using a Thomas algorithm to solve the matrix serially. I found a ...
1
vote
1answer
64 views

LAPACK DGGEVX: BALANC option

I'm using DGGEVX routine from LAPACKE with BALANC option as shown below, but to my surprise changing BALANC option from 'N' to ...
0
votes
1answer
140 views

How to give a simple estimation of errors for results obtained from 4th order Runge-Kutta

This question is a follow up of another one I have asked a while ago. I have successfully implemented my problem using odeint library and I get the results I expect. However I would like to give an ...
1
vote
0answers
635 views

Can you provide me with the source code of DMRG writen by C++?

I want to study the Density matrix renormalization Group(DMRG). Can some one provide me with the souce code which is writen by C++ for study purpose only? The code is not necessiary very professional, ...
3
votes
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"...
-2
votes
1answer
295 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-...
1
vote
1answer
828 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) $ $ \...
3
votes
1answer
335 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
votes
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
votes
1answer
993 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 ...
0
votes
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 ...
0
votes
1answer
420 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
votes
1answer
397 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 ...
2
votes
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: ...
0
votes
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
484 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
votes
2answers
244 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 ...
7
votes
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: ...