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Questions tagged [c++]

A powerful object oriented programming language.

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0answers
47 views

Problem with rate of convergent of numerical scheme for hyperbolic conservation law

I need help to verify my code in C++ that developed to solve the Burgers equation $$\\u_t + (\frac{u^2}{2})_x =0$$ $$u(x,0)=\sin(\pi x),\text{ } -1\leq x \leq 1$$ using a third-order ...
2
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1answer
102 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 ...
1
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1answer
39 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
votes
3answers
121 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 ...
8
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1answer
109 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 ...
4
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2answers
404 views

overflow upper incomplete gamma function

I want to calculate the following equation: $$\frac{\theta \Gamma \left(\kappa+1,\frac{o}{\theta }\right)-o \Gamma \left(\kappa,\frac{o}{\theta }\right)}{\Gamma (\kappa)}+o+s$$ with $s>0, o>0, ...
16
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2answers
1k 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 ...
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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2answers
685 views

2D Ising Model, heat capacity decreases with lattice size

The problem I'm trying to make a metropolis simulation of the 2D Ising model. Basically, it's the following, for each monte-carlo step: Visit each lattice site, Compute energy required to flip ...
1
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0answers
39 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
47 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 ...
2
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0answers
33 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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68 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: ...
8
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9answers
837 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 ...
1
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0answers
108 views

C++ Library: What is the Most Efficient Library that Factorizes a Polynomial?

I need to know what library is the fastest one that can factorize a polynomial of large degree whose coefficients are big integers. I have tried NTL library to factorize a monic polynomial but it is ...
3
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0answers
38 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 ...
17
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3answers
2k 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 ...
2
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1answer
80 views

Automatic differentiation via ADOL-C and the Heaviside Function

I am writting a c++ program in which I define a function $$\displaystyle F(t) = \sum_{i}r_i\,H(t-t_i)$$ where $H$ is the heaviside function, $t_i$ are optimal parameters which are mutable. The ...
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1answer
52 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 ...
4
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0answers
218 views

Adaptive mesh data structure for Fast Marching Method to overcome RAM limit

On an uniform mesh of positions in space $\ (x_i,y_j,z_k)$: $$\ x_i = x_0 + i\Delta x,\quad i=0,\ldots,n_x$$ $$\ y_j = y_0 + j\Delta y,\quad j=0,\ldots,n_y$$ $$\ z_k = z_0 + k\Delta z,\quad k=0,\...
1
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3answers
248 views

Traveling Salesman Problem

First off some context. The Traveling Salesman Problem(TSP) is to find the most efficient route passing through a series of points only once. However, there is no perfect function to solve for this in ...
2
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2answers
179 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 ...
36
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7answers
9k 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. ...
11
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3answers
818 views

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 ...
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0answers
35 views

Metis: how to use and tutorial recommendation

I am new to METIS and trying to use it in my fortran code. I read the manual online. But still, I am not sure about how to implement it my code. I tried the test cases in the graphs directory. For ...
3
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2answers
489 views

I am searching for a C++ code implementing the complex polygamma function

I googled about some code on the complex polygamma function especially C++ code, but can't find anything. Does anyone know where to find such code? The complex digamma function does exist but not the ...
2
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1answer
70 views

How to justify using available code (in different language) for comparing algorithms

I have proposed an algorithm for a scheduling problem in a submitting paper. In the revision, the reviewer asked us to compare with another algorithm from the literature. Our algorithm is in MATLAB, ...
0
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1answer
87 views

Good C, C++ library for efficient grid search / tuples, ideally with bindings to Eigen

I have a $q$-dimensional grid, known at run, not compile-time, that has $50$ points in each direction and hence $50^3$ combinations that I would like to first build and then call a function with each ...
4
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3answers
257 views

Best software to do big number calculations quickly

I am trying to do some work on some math conjecture. I am testing the conjecture numbers using very large math numbers (100+ digits ). I am currently using python to test these numbers. In the ...
1
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0answers
45 views

How to integrate the contents of a vector using an adaptive quadrature routine [duplicate]

I have a function which requires the return type to be a container. The problem is that I need to integrate the contents of the container as efficiently as possible and was hoping to use adaptive ...
5
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1answer
127 views

Whittaker-Shannon interpolation: Accuracy dies with speedup; can it be fixed?

With a truncated Whitaker-Shannon series (cardinal series) $$ f(t) = \sum_{j = 0}^{n-1} y_{j} \frac{\sin\left(\pi( \frac{t-t_0}{h} -j)\right)}{\pi\left(\frac{t-t_0}{h}-j\right)} $$ we can naively ...
1
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2answers
2k views

Solving the 1D Particle-in-a-Box using C++

I've just finished learning the physics behind the problem and would like to write a program in C++ than can solve the problem. I'm actually stuck at the start. I've quite a bit of research, the ...
2
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3answers
146 views

Find a solution of large system of inequalities

I have a large system of homogenous inequalities involving 33 real unknowns of the form $$ \vec{F}(z_i)^T \cdot \vec{X}>0\, $$ where $\vec{X} = \left(x_1,...,x_{24}\right)^T$ are the unknowns and ...
1
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1answer
169 views

LAPACK equivalent on c++ , which is the best one? [duplicate]

I am following a course of computational material physics. The professor uses fortran to code and uses lapack to solve eigenvalue problems. So far I just know c++. There is an equivalent library that ...
3
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2answers
1k views

Developing a C++ solid mechanics program

I am a beginner in computational science and programming. I am doing research in non linear solid mechanics analysis and using C++ for coding. I have been exploring various finite element open source ...
3
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0answers
60 views

Structural Analysis Library

Can anyone recommend a structural analysis library that satisfies the following requirements: C++ API Simulate both beam elements and shell (slab) elements Both static and dynamic analysis Free and/...
0
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0answers
261 views

OpenCV: How to get the “rectified” fundamental matrix?

I have a stereo image pair and the respective intrinsics and extrinsics of both cameras. With this information, I can calculate the fundamental Matrix between the two cameras (let's call it F). I can ...
3
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3answers
269 views

Simple way to store/read data from file in C++

I've been running various simulations with C++, and doing so has often involved saving lots of data to file (real/complex matrices, arrays, etc) and then reading them into other programs later. ...
2
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0answers
1k 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 ...
5
votes
2answers
244 views

Recommended language/environment for large scale semi-continuous biological models

We have a fairly large (maybe 1000 equations) differential-algebraic equation model written in ACSLX, an obsolete modelling environment similar to Modelica. The model represents the evolution of a ...
2
votes
2answers
254 views

Integration of a diverge function in c++ GSL Library

I am trying to perform an Integral of Hypergeometric function 2F1(a,b,c,x) from -1 to 1 for some good values of $a,b,c$ (lets say $a=1,b=2,c=3$) . I did it in ...
8
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3answers
2k 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 ...
9
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3answers
2k views

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 ...
3
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2answers
116 views

C++ library to mutate pdb residues

Are there any open source libraries available to mutate PDB protein residues? If so are do you have any examples of them?
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0answers
48 views

FFTW on subarray with MPI

With the guru interfaces of FFTW, I can apply transforms only to parts of a multidimensional array by modifying the fftw_iodim ...
1
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3answers
879 views

C++ mixed integer nonlinear programming (MINLP) solver

Doing research project in material involving (mixed integer nonlinear programming) MINLP problem, we want to implement MINLP based on C++, because the majority of our project is based on C++. What ...
1
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2answers
438 views

How does MPI differentiate between two computers?

I am starting to dabble in MPI. I am fairly new to this area and I am currently reading the MPI standard. I would like to write my first MPI program, a simple hello world program, on a cluster that ...
3
votes
2answers
1k views

Stabilizing a 3x3 real symmetric matrix eigenvalue calculation

I have many 3x3 real symmetric matrices for which I need to determine the eigenvalues. Wikipedia gives a nice non-iterative algorithm for this case, which I have translated into C++: ...
0
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2answers
754 views

Does armadillo library slow down the execution of matrix operations?

I've converted a MATLAB code to C++ to speed it up, using the Armadillo library to handle matrix operations in C++, but surprisingly it is 10 times slower than the MATLAB code! So I test the ...
1
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0answers
99 views

$ A * B $ computation when B is a symmetric matrix in armadillo [closed]

Is there any way to multiply a symmetric matrix by a dense one in armadillo(and use the fact that we have a symmetric matrix)? I know about DSYMM Routine in BLAS,...