Questions tagged [c++]
A powerful object oriented programming language.
2
votes
0answers
25 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 ...
0
votes
1answer
34 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 ...
2
votes
2answers
168 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 ...
2
votes
1answer
54 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 ...
1
vote
0answers
21 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 ...
2
votes
1answer
65 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, ...
1
vote
0answers
44 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 ...
0
votes
1answer
71 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 ...
5
votes
1answer
108 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
vote
1answer
130 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 ...
2
votes
3answers
134 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 ...
3
votes
0answers
52 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
votes
0answers
133 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
votes
3answers
138 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. ...
17
votes
3answers
1k 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 ...
4
votes
3answers
252 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 ...
2
votes
0answers
710 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 ...
1
vote
0answers
44 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
vote
0answers
85 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,...
-1
votes
2answers
549 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 ...
5
votes
3answers
726 views
Efficient eigen-decomposition of covariance matrix
I am looking for an C/C++/Python algorithm implementation that calculates eigenvalues and eigenvectors of a symmetric, positive semidefinite covariance matrix.
A general-purpose eigen-decomposition ...
0
votes
1answer
122 views
Looking for a converter of AMPL/GAMS models into C code
I've done an extensive web search, but could not find an option. Conversion between model formats is available, but conversion of objective function and constraint equations into C code seems absent. ...
2
votes
2answers
190 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 ...
2
votes
1answer
161 views
MD Simulation: Reference for the Neighbor's List Method
With a rather basic knowledge in C++, I have written my own MD simulation code. Currently, I calculate forces in the most naive way: I go through all the atoms and account for their interactions. This ...
1
vote
0answers
54 views
Dense decomposition of very non-square matrices
I have inherited code that solves Eigen::Matrix problems using the code shown on this page:
...
0
votes
1answer
324 views
I've developed a derivative-free optimization method, looking for comments
Here is the URL: https://github.com/avaneev/biteopt
I've tested it on numerous global optimization benchmarking functions (included), and on real-world hyperparameter optimization problems I have. ...
2
votes
0answers
52 views
Looking for a version of DSDP that is less prone to integer overflows than the original
I am working on a problem that involves semidefinite programming (constrained optimization of fairly large positive definite matrices). The software is written in C++ and calls DSDP 5.8 to solve the ...
1
vote
2answers
511 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 ...
0
votes
1answer
60 views
Wanting an explanation of the variables in Iterative PCA algorithm
I've been trying to implement the CPU GS-PCA algorithm in this paper .
The code starts on page 28
I have a program written a script in python which gives the same output as the C++ program in the ...
0
votes
1answer
27 views
combinatory exploration c++ [closed]
I have n spots with 2 possible positions each.
I would like to explore all of this possibilities in C++ using loops (or something else if there is a better option).
I was thinking of looping from 0 ...
1
vote
2answers
952 views
Physics Simulation in C++
OK, I know a bit of C++ (very basic syntax), and I want to do physics simulation in C++, like stuff like (also the things mentioned here):
Ripples and waves over a 2-d surface
Vibrating string/...
1
vote
1answer
189 views
C++: Efficient library for dense linear algebra operations (determinant & principal minors)
I usually work with Python, but my basic knowledge of c++ allows me to switch when I need to increase the speed of my code.
Currently, I have a python script that (among other things) computes the ...
0
votes
1answer
109 views
How to do a Generalized Complex Schur (or QZ) Decomposition with Eigen C++? [closed]
I would like to do a Generalized Schur (or QZ) decomposition for a pair of complex matrices $A$ and $B$.
I found the following class:
...
5
votes
2answers
222 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
0answers
137 views
What could be causing multi-dimensional numerical integration inconsistency?
I'm trying to numerically integrate a multi-dimensional expression. The integrand is complicated; for example this is the integrand for $N=4$:
$$\begin{aligned}&x_1^6x_2^5x_3^3x_4^2(x_1-x_1x_2)(...
0
votes
1answer
84 views
Is the time step size of a Rosenbrock method for stiff systems iteratively calculated?
I have an ODE system of the general form
y' = k(y)(x) + q(z)(x)
x' = a(z)(x) + b(x)(x)
where k,q,a and b are also dependent on the states x and y. The ...
6
votes
2answers
150 views
Generating set of points on a surface defined by constraint
I'm writing a differential geometry library, and one minor convenience I'd like to offer is to generate a set of points on a surface given by a constraint. For example, for a sphere,
$$x^2+y^2+z^2-r^...
1
vote
0answers
209 views
Newton - Raphson method : maxima of function in 2 variables
I am computing the maximum of a function (with two-variables) using Newton-Raphson method. The function is : $e^{-(x \ - x_0)^2 - (y \ - y_0)^2}$, whose maxima exists at $(x_0,y_0)$.
The Jacobian ...
1
vote
2answers
286 views
C++ template design pattern for groups (algebra)
Having both programmed my share of c++ and studied some beginners group theory some year ago, I got curious about this...
Is there any particularly popular template based (object oriented) design ...
1
vote
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 ...
1
vote
2answers
174 views
Inverting big symmetric and singular matrices
In this post I found a very similar probem to the one I have, but not a satisfactory answer for my purposes.
I have a set of matrices $C_\ell$. They are exactly symmetric by construction. ...
2
votes
0answers
312 views
Using C/C++ for Markov chain Monte Carlo (MCMC) methods
I'm working on optimizing the parameters of a mathematical model to fit experimental data, using an existing formula for the likelihood of observing the data given a set of parameter values. At the ...
4
votes
1answer
128 views
Simple Monte Carlo in C++, result dependent from seed
I implemented as an exercise a program to sample the statistics of the escape time of a Brownian particle in a potential well. I used the Euler-Maruyama method to numerically integrate the ...
0
votes
1answer
512 views
Speeding up ODEINT stiff example [closed]
I am trying the implement the following odeint solver example but my differential equations are different.
https://github.com/headmyshoulder/odeint-v2/blob/master/examples/stiff_system.cpp
The ...
1
vote
2answers
148 views
Sign of integer determinant 4 by 4
I'm in the context of this publication: http://www.gilbertbernstein.com/resources/booleans2009.pdf
I applied quantization to my point coordinates: All coordinates are integer lying in [0, 2 power 20]....
4
votes
1answer
118 views
Using GSL for basic operations
I am learning C/C++ for Scientific Computing and I have a question regarding the usage of scientific libraries for basic operations.
Suppose I have to write a small program in C for a bioinformatics ...
4
votes
1answer
486 views
2D numerical integration with infinite limit (C++)
In order to integrate a two dimensional function of the form
$$\int_{1}^\infty \int_{-\sqrt{x^2-1}}^{\sqrt{x^2-1}} e^{-x} \rm{d}y \rm{d}x,$$
I have been attempting to use the following code (written ...
1
vote
1answer
333 views
LAPACK sorting eigenvalues differently each time
I'm using LAPACK zgeev routine to get eigenvalues and eigenvectors of a symmetric matrix in C++. Problem is zgeev is being called in a loop but it sorts eigenvalues (and eigenvectors) differently ...
1
vote
0answers
86 views
MPI_Finalize() only some processors
I want to develop a distributed algorithm with MPI which have load balancing capability. But there is a situation that I'm not very clear about, which is, when the number of tasks is less than the ...
0
votes
2answers
241 views
Matlab, Mathematica & LAPACK returning 3 different eigenvectors
(I'm not sure which of math.se / stackoverflow / scicomp.se is the right place to ask this question)
I have a C++ code which generates a complex matrix and then calculates its eigenvalues and ...
