Questions tagged [c++]

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High quality constrained optimization C++ library with matrix free second order solver?

I'm working with large scale constrained optimization problem. Some of my constraints can be non linear. Currently i'm using IPOPT. Quality is good by my Hessian computation too slow. It seems that i ...
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2answers
114 views

Evaluation of real-valued confluent hypergeometric function with specific complex arguments

In my C++ code, I need to evaluate the confluent hypergeometric function ${}_1F_1(a,b;z)$ with complex arguments in a special case. More precisely, I have to compute $$ e^{-i\phi}{}_1F_1(\ell+1+iZ,2(\...
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1answer
97 views

C++ Eigen::Map class questions

The Eigen::Map documentation here (https://eigen.tuxfamily.org/dox/classEigen_1_1Map.html) mentions the following: This class represents a matrix or vector expression mapping an existing array of data....
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51 views

Why does Eigen allocate a temporary to evaluate A.noalias() = B.transpose()*C in parallel?

I wrote a program which iteratively transforms data using matrix multiplications. To minimize the number of large memory allocations, I use two roughly equal-sized ...
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1answer
149 views

Perturbation problem using Runge-Kutta 4

I'm trying to evaluate the perturbations magnitude between 2 body orbiting a central one in three dimensions. In order to do this I need to have an estimate of the error, which I did using Richardson ...
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1answer
248 views

Reference request: C++ and numerical analysis book

I'm a master student with a good Numerical analysis background. I'm going to do a master thesis in the same subject, but I need to use C++ since my advisor loves it, and I also believe it's the best ...
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2answers
104 views

Need software for generating self-avoiding random walks on a tetrahedral lattice

I am looking for FOSS code that can generate self-avoiding random walk trajectories on a tetrahedral lattice. The purpose of the exercise is to create random conformations of model polymer chains that ...
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1answer
36 views

MPI_Test not progressing MPI_Isend/MPI_Irecv requests

I am running a CFD simulation with a 200,000-vertex mesh. I've decomposed the mesh into 2 load-balanced sub-domains to test my parallel implementation. In the specific function that I am time-...
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1answer
87 views

Point cloud to height map in C++

With the increased popularity of 3D imaging and scanning I thought it would be easy to transform a xyz point cloud into a Height Map (xy matrix of z points), but after a couple of hours searching I ...
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0answers
40 views

N-body correct scaling

I realized an usual way to scale an N-body problem for an N-body simulation is by choosing units such that gravitational constant $G = 1$, but I'm probably doing it the wrong way. Suppose I simply ...
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2answers
171 views

Using the BDF and RK4 methods to solve this coupled system of ODEs in C++

I'm trying to solve a system of ODEs using the BDF order 4 method. I find the first 3 points using RK4, then for the implicit part of the BDF, I use Newton-Raphson iteration. Unfortunately my solution ...
2
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1answer
163 views

Can one safely use an OpenMP parallel loop with Armadillo?

I have a C++ code performing some Armadillo computations in a loop. I'd like to parallelize this loop with OpenMP. But Armadillo automatically uses OpenMP for some computations. So, would the OpenMP ...
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1answer
104 views

Range of a matrix from its complete orthogonal decomposition

In this StackOverflow answer, @Gokul has shown how to get a basis of the kernel of a matrix with the help of the 'Eigen' function CompleteOrthogonalDecomposition. ...
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0answers
124 views

Optimize speed for calculating the approximate inverse of a large matrix

I am searching for a faster method to calculate an approximate inverse of a large matrix (up to 32000x32000) resulting from a discrete non-linear system of partial differential equations. I'm using C++...
3
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1answer
313 views

'Eigen' matrices with static dimension

I noticed that 'Eigen' matrices with dynamic dimension are less efficient than the matrices with static dimension. My algorithm uses a lot of matrices which don't need to be resized, so I wanted to ...
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82 views

Ill-conditioned stiffness matrix

I am writting a Fem code in c++ for a 2d plane stress model. My question is regarding the assembly stiffness matrix.I noticed that some elements of the matrix are not exactly zero but insted a number ...
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0answers
297 views

Which library to use in C++ for fast DCT's?

I need to apply a 1D type-II DCT (Discrete Cosine Transform) to each column of a matrix while normalizing the result in C++. Effectively, I want to multiply my matrix with an orthogonal type-II DCT-...
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44 views

Jacobi Gauss-Seidel Method

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105 views

Computing Singular Value Decomposition of small ($4\times 4$) matrices

I need to compute the Singular Value Decomposition (SVD) of many $4 \times 4$ matrices. I'm looking for SVD algorithms specialized for small matrices. I've read that the ...
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46 views

Triplet optimization algorithm producing weird results?

I wrote an algorithm for data analysis using the CERN ROOT framework. It takes in three files of sorted UNIX timestamps from a single year and pairs them up in the closest triplets, where each file ...
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1answer
97 views

Extracting data from VTK simulations using C++

I have been given a few numerical simulations regarding fluid mixing and have been asked to extract a few parameters from them using C++. Altogether there are about 1000 VTK files per simulation, and ...
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1answer
358 views

Reading VTK file into C++ for analysis

I apologize in advance if this post is at all ignorant or elementary, I am a pure mathematician who is newly getting into the world of scientific computing. For my research, my advisor would like me ...
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1answer
152 views

How to calculate error in successive over relaxation for PDE?

I am trying to solve the Poisson equation numerically using the FDM method in C++. But I have a little confusion with the iterative process. I understand that the number of iterations should go until ...
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1answer
162 views

Calculating the Strange Attractor of the Duffing Oscillator in C++

I am simultaneously trying to learn computational physics methods, chaos, and C++. I think this is the right site for the question, and I apologise if not. I started working through Thijssen's ...
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3answers
236 views

How to begin writing scientific codes in C++ in Trilinos or PETSC style?

My background: I have taken some courses on numerical analysis during my PhD and read a few books on the topic as well. I mostly work on low Reynolds number fluid mechanics and use boundary element ...
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1answer
1k views

How to document math formulations in scientific computing codes?

I am writing the code relate to math. There is some complicated math formulation in the project. Directly writing the calculation code leads to hard understanding; thus I want to comment on the ...
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0answers
28 views

CUDA and implicit array expansion

I am retrying this question since I didn’t do so properly last time: I have implement a simply c++ CUDA example that takes A [m x 1] and B [1 x N] and adds them element wise with what I am used to ...
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69 views

Calculating the exponential of a complex matrix

I am trying to calculate the exponent of a 3 x 3 matrix using the formula $\sum_{i=0}^\infty\frac {A^n}{n!}$ I believe that my error may lay in the scalar division with a factorial or the member ...
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1answer
202 views

Finite Difference libray C++

What is the best FD library (or collection of libraries) for C++ codes? I am looking for some data structure implementation that offers the possibility to do parallel computations on adaptively ...
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1answer
136 views

Suggestions for scientific computing projects to undertake to sharpen core skills

Currently I am completing all exercises in books like "Introduction to Python for Science and Engineering, David Pine" and "Guid to Scientific Computing in C++, Pitt-Francis, Whitley". I am looking ...
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0answers
71 views

Whi are chi-squared distributions in (C++) boost::random and C++ STL faster than in boost::math?

I am trying to generate random chi-squared numbers in C++, according to some degree of freedom (which can be a float). Several libraries can be used for that purpose, among which the C++11 Standard ...
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3answers
121 views

How to store a TB size array in C++ on a cluster

I want to do a huge simulation that requires ~ 1 TB of data to describe a bunch of interacting particles (each has different interactions). Is it possible to store this data in an array in C++, so ...
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1answer
342 views

C++ book recommendation- Scientific computing and C++

I'm a master's student in Math interested in Numerical Analysis. I know there are lots of questions like that on this site, but I think this is the best place to ask. So, I'm looking for an ...
2
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3answers
463 views

Generating Random Orthogonal Matrices in C++

I'm looking for an open-source library for the generation of random n-dimensional orthogonal matrices in C++. In python, it looks like such a function is available in the NumPy package. But I was not ...
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1answer
133 views

Is C++ and Object-Oriented Numeric Computing for Scientists and Engineers by Daoqi Yang still relevant?

I'm looking to learn C++ primarily from a scientific computation perspective. The approach of the textbook seems ideal to me as it covers C++ from first principles with an emphasis on numerical ...
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2answers
376 views

What are new c++20 features that are relevant to scientific computation?

In my research department we plan a small seminar on the new c++20 language standard. There are exhaustive lists online presenting the new features of the language standard, some of which will be of ...
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2answers
135 views

Writing code on the CPU while developing, running it on the GPU when live - which approach?

In my simulations I am using dense matrix-vector multiplications and 2D-fft transformations quite often, for matrix sizes of 8kx8k and up. Hence, I assume that using a GPU is beneficial for speeding ...
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1answer
77 views

Using adolc for the sign function in c++

Here is an implementation of the sign function in C++ using Adolc librairy for automatic differentiation. ...
3
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1answer
343 views

The Formula of Explicit Runge-Kutta Fourteen order

I need an explicit Runge-Kutta 14th order formula. If you know about some reference that discusses at least 10th order (or higher, since I'm looking for the 14th) of Runge-Kutta and there is ...
2
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1answer
248 views

How to perform an eigendecomposition of a general complex matrix with arbitrary precision in C/C++

I need to obtain the Eigenvectors of a general complex matrix, but with quadruple precision. Is anyone aware of a means to do this? I currently use Tux Eigen, and I see that in their unsupported ...
2
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1answer
111 views

Gmsh meshes flat faces incorrectly for cylindrical faces

I have some C++ code that generates meshes from step files and then analyses these meshes for visibility of the faces from different viewing directions. I currently use CGAL but I would like to switch ...
3
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3answers
161 views

GPGPU computing, software selection

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 ...
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1answer
1k views

Is using std::valarray considered good practice?

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 ...
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0answers
90 views

How to deal with a huge system of ODEs in Boost ODEINT?

I am using the C++ library ODEint, which is part of Boost, to solve an extremely large system of coupled ODEs - in particular 1975 equations with large rational functions in the coefficients. In the ...
3
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1answer
71 views

PETSc - Manipulate BAIJ matrix locally

My program loads a parallel PETSc matrix $A$ on several MPI processes, each holding a block submatrix $A_i$. I would like to retrieve the local submatrix $A_i$, the one corresponding to the current ...
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0answers
39 views

Algorithm to join hexahedra and obtain outline volume

I would like to join several hexahedra and obtain an outline volume. First, I started with 2D implementation. In 2D, there are non-intersecting quadrangles which always touch each other as shown in ...
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0answers
111 views

How to read data from simply formatted text file (c++)?

Mesh information like points, faces and cells is to be stored into separate files: e.g. for points file: # points data: x y z N_Points 100 x1 y1 z1 x2 y2 z2 ... cell file: # cells data: ...
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0answers
140 views

Derivative of Whittaker-Shannon interpolant

Last time we looked at how to improve the accuracy of Whittaker-Shannon interpolation, where user njuffa demonstrated that judicious use of sin_pi could greatly ...
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1answer
196 views

Computing excited states using itensor (with DMRG)

I am trying to compute first few excited states of some Hamiltonian (I am using itensor and its DMRG algorithm). To do so, I am ...
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2answers
352 views

Compiled c++ code runs much faster with double than float. Explanation?

I am still rather new on here and I hope question is suitable for this forum otherwise please help me migrate it to greener pastures. I am an electrical engineer specializing in applying mathematics ...

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