Questions tagged [c++]
For questions about writing C++ computational code or utilizing libraries written with C++.
328
questions
66
votes
13
answers
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C++ vs Fortran for HPC
In my computational science PhD program, we are working almost exclusively in C++ and Fortran. It seems like some professors prefer one over the other. I am wondering which one is 'better' or if one ...
- 2,119
57
votes
7
answers
22k
views
Is it a good idea to use vector<vector<double>> to form a matrix class for high performance scientific computing code?
Is it a good idea to use vector<vector<double>> (using std) to form a matrix class for high performance scientific computing code?
If the answer is no. ...
- 603
30
votes
5
answers
2k
views
What features do users need from an MPI C++ interface?
The 3.0 version of the MPI standard formally deleted the C++ interface (it was previously deprecated). While implementations may still support it, features that are new in MPI-3 do not have a C++ ...
- 2,116
29
votes
9
answers
2k
views
What is a good way to run parameter studies in C++
The problem
I'm currently working on a Finite Element Navier Stokes simulation and I would like to investigate the effects of a variety of parameters. Some parameters are specified in an input file ...
- 495
29
votes
10
answers
22k
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 ...
28
votes
9
answers
4k
views
Modern C++ in scientific computing?
I am looking for books or articles, or blog-posts, or any published material in general, that address specifically the uses of C++ modern features (move semantics, the STL, iterators, lazy evaluation, ...
- 1,729
25
votes
5
answers
6k
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.......
- 353
25
votes
4
answers
3k
views
When should I use C++ expression templates in computational science, and when should I *not* use them?
Suppose that I'm working on a scientific code in C++. In a recent discussion with a colleague, it was argued that expression templates could be a really bad thing, potentially making software ...
- 30.3k
22
votes
7
answers
4k
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 ...
- 323
19
votes
6
answers
3k
views
To what extent is generic and meta-programming using C++ templates useful in computational science?
The C++ language provides generic programming and metaprogramming through templates. These techniques have found their way into many large-scale scientific computing packages (e.g., MPQC, LAMMPS, CGAL,...
- 1,042
19
votes
3
answers
11k
views
C++ Best practices for dealing with many constants, variables in scientific codes
I am developing a code to simulate fluid flow with biological substances present in the flow. This involves the standard Navier-Stokes equations coupled to some additional biological models. There are ...
19
votes
5
answers
3k
views
Parallel Scientific Computation Software Development Language?
I want to develop a parallel scientific computation software from scratch. I want some thoughts on which language to start. The program involves reading/writing data to txt files and doing heavy ...
- 343
16
votes
3
answers
2k
views
Why would a computational scientist need to implement their own version of std::complex?
Many of the better-known C++ libraries in computational science such as Eigen, Trilinos, and deal.II use the standard C++ template header library object, ...
- 6,931
16
votes
2
answers
2k
views
Boost::mpi or C MPI for high performance scientific applications?
The thing I dislike most about MPI is dealing with datatypes (i.e. data maps/masks) because they don't fit that nicely with object oriented C++. boost::mpi only ...
- 1,075
15
votes
2
answers
8k
views
solve $xA=b$ for $x$ using LAPACK and BLAS
I am porting an existing code from MATLAB to C++ and have a linear system to solve $xA=b$ (rather than the more typical form $Ax=b$)
The matrix $A$ is dense, and of general form, but is no larger ...
- 253
14
votes
4
answers
4k
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 / ...
- 277
14
votes
2
answers
510
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 ...
- 2,627
13
votes
5
answers
987
views
Compute $(e^x-1)/x$ near $x = 0$
The function $f \colon x \mapsto (e^x-1)/x$ has singularity near $x = 0$. That singularity can be lifted, though: for $x = 1$, one should have $f(x) = 1$, since
$$
e^x = \sum_{k=0} \frac{x^k}{k!}
$$
...
- 233
13
votes
3
answers
1k
views
Blaze linear algebra library?
The paper "Expression Templates Revisited: A Performance Analysis of Current Methodologies" in SIAM Journal of Scientific Computing references the "Blaze" linear algebra library. I haven't heard of it ...
- 805
12
votes
3
answers
1k
views
Efficient tridiagonal matrix algorithm implementation
I am solving a physical problem using implicit numerical scheme. This leads me to solving a linear equation with tridiagonal matrix. I've coded this algorithm from Wikipedia. I wonder if there is an ...
- 455
12
votes
1
answer
871
views
Replacing Mathematica's QuasiMonteCarlo integration in C++
I have a Mathematica program which performs some integrals in 3 or 4 dimensions using the QuasiMonteCarlo method. The problem is, it takes an annoyingly long time ...
- 3,373
11
votes
1
answer
11k
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 ...
- 113
11
votes
3
answers
1k
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Testing if two 12x12 matrices have the same determinant
I am given a $12 \times 12$ matrix $Q$ that is symmetric, invertible, positive definite and dense. I need to test if $$\det(Q) = \det(12I-Q-J) \; \; (1)$$ where $J$ is the all ones matrix.
I am ...
- 458
11
votes
2
answers
17k
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C++ library for nonlinear constrained minimization
I am currently trying to solve nonlinear constrained minimization problem as implemented in matlab "fmincon" function. My expectations are, minimize(fun1,x0,uB,lB,fun2) where x0 is initial state, fun1 ...
- 111
10
votes
6
answers
1k
views
Where does Python fit into the picture within computational science field?
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 ...
- 593
10
votes
3
answers
2k
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Are there any "light-weight" FEM packages around?
Basically, FEM seems to be a problem that is pretty much "solved". There are numerous powerful frameworks existing, like Trilinos, PETSc, FEniCS, Libmesh or MOOSE.
One thing they have in common: They ...
- 1,463
10
votes
3
answers
4k
views
How to build a recursive spline function in C++
At the moment I am working on a differential equation solving method called basis-spline collocation. What I am having trouble with is building a method to build an arbitrary order spline, with the ...
- 101
10
votes
3
answers
3k
views
How to use polylogarithm function in c++?
Is there any preprocessor directives that could be used to use the polylog function? Or is it included in cmath? If so, do you call it by Li or by polylog?
EDIT:
What I really am trying to do is give ...
- 309
10
votes
1
answer
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 ...
- 323
10
votes
5
answers
9k
views
C++ library for numerical intergration (quadrature)
I have my own little subroutine for numerical integration (quadrature), which is a C++ adaptation of an ALGOL program published by Bulirsch & Stoer in 1967 (Numerische Mathematik, 9, 271-278).
I ...
- 258
10
votes
1
answer
720
views
What is the impact of C++11 move semantics in the context of scientific computing?
C++11 introduces move semantics which can, for example, improve code performance in situations where C++03 would need to perform a copy construction or copy assignment. This article reports that ...
- 495
10
votes
1
answer
3k
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 ...
- 54.1k
10
votes
0
answers
333
views
Numerical integration using interval arithmetic, nowadays
Is there now a package for rigorous numerical integration that uses interval arithmetic and has access to a well-developed library of special functions?
By "well-developed", I mean something that, at ...
- 269
9
votes
6
answers
13k
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 ...
9
votes
10
answers
5k
views
9
votes
4
answers
530
views
Hosting site for a small scientific library
For my research work I have been developing a small C++ library aimed at facilitating the communication between C++ computational codes and Octave/Matlab (when the latter is used for post-processing ...
- 313
9
votes
3
answers
2k
views
Recommendations for a lightweight/no-install C or C++ based dense linear algebra solver
Most of my programming is one-off research codes in C for my own use. I have never distributed any code to other than close collaborators. I have developed an algorithm that I am publishing in a ...
- 193
9
votes
1
answer
741
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 ...
- 397
9
votes
2
answers
1k
views
Library with polylogarithm function [duplicate]
I am looking for a reliable library where I can find polylogarithm function and newton/secant method for solving non-linear equations. Basically I have something like this:
...
- 191
8
votes
9
answers
1k
views
Do I need to learn C?
I am a PhD student in Scientific Computing and over the past few months, I spent a good amount of time learning Python and C++ the right way. I feel that I have learnt C++ well and I can use Python to ...
- 3,344
8
votes
4
answers
6k
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 ...
- 1,879
8
votes
2
answers
9k
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 ...
- 322
8
votes
1
answer
2k
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 ...
8
votes
1
answer
831
views
C++ library for graphs with maximum common subgraph solver
I'm looking for a convenient, free C++ library for graphs that include a solver for the maximum common subgraph (MCS) problem.
I'm aware of the
Boost Graph Library
and
LEMON
, but neither includes an ...
- 1,042
8
votes
3
answers
8k
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?
...
- 1,075
8
votes
0
answers
4k
views
Good C++ optimization library for BFGS
To implement maximum likelihood estimators, I am looking for a good C++ optimization library that plays nicely with Eigen's matrix objects. Eigen has some capability of interfacing of its own but if ...
- 183
7
votes
4
answers
8k
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....
- 309
7
votes
3
answers
4k
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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. ...
- 193
7
votes
2
answers
670
views
Recommendations for a usable, fast GPL-compatible derivative-free numerical optimization library that can be interfaced to C++
I am dealing with optimization of functions for which I do not have derivatives available, and the optimization is not constrained. I am searching for a high quality GNU Public License-compatible ...
- 1,916
7
votes
2
answers
759
views
transitive floating point comparison with (absolute) tolerance
I want to compare two floating point numbers for equality relative to a known absolute tolerance. However, this is inside an algorithm I wrote quite some time ago, and I believe the logic of that ...
- 2,141