Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [c]

C is a general purpose programming language. Originally intended for implementing system software, C and its close relatives are the principle languages used in most modern operating systems. Due to its thin layer of abstraction and low overhead, C allows efficient coding of algorithms and data ...

1
vote
1answer
50 views

Wrong result of 'ddot' from BLAS

I am having trouble with a C/C++ program that uses the BLAS routine ddot. I am running Linux and so far LAPACK routines worked without any problems. I get a wrong ...
3
votes
3answers
111 views

How good are current implementations of rand() in C?

There is a lot of literature that indicates using rand() for simulations might be harmful. A couple of them are as follows: https://www.sciencedirect.com/science/...
0
votes
1answer
97 views

MPI data broadcast or not in C

I have two slightly different but getting the same results MPI code. The first one is from an open-source package having several data exchange steps in between: ...
1
vote
1answer
65 views

Problem with 'dsysv' from LAPACK

I am having trouble with a C program that uses the function dsysv from LAPACK. Everything compiles and works without any errors, my only problem is, that the ...
4
votes
3answers
280 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
72 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. ...
0
votes
1answer
271 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
47 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 ...
2
votes
0answers
78 views

Use of multidimensional FFTW and normalisation factor

I am using the FFTW MPI in C. I have a simple question. Quoting from fftw.org The multi-dimensional transforms of FFTW, in general, compute simply the separable product of the given 1d ...
1
vote
0answers
142 views

Potential gain - Matlab vs C/C++ - assembly and eigenvalues

I have a Matlab code computing the solution to an eigenvalue PDE. It consists of two parts: assembly of the stiffness/rigidity matrices and solving a generalized eigenvalue problem. I mention that the ...
0
votes
1answer
190 views

High precision Discrete Fourier Transform in c

I'm trying to do a high precision discrete fourier transform on a signal. To examine the precision, I use a gaussian function as the signal, because the fourier transform is also a gaussian function. ...
3
votes
0answers
196 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
103 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 ...
1
vote
2answers
138 views

How to deal with big numbers in intermediate calculations?

I have a rather long expression (https://pastebin.com/jUsxdCCs) that is an analytical solution of a set of differential equations generated symbolically from Maple. I need to solve a set of equations ...
1
vote
0answers
59 views

lightweight implementation of semiempirical quantum chemistry (e.g. MNDO,AM-1,PM3)

I'm searching for semi-empirical quantum chemistry solver which would be easy to integrate into my own software. I found a few implementations which can be in principle used e.g. MOPAC, ORCA, SQM some ...
2
votes
0answers
119 views

minimalistic library for classical molecular mechanics force-field in C/C++/Python

I would like some classical molecular mechanics forcefield library or super-simple program which does not have any external dependences, so that I can plug it into my software without worry of "...
2
votes
1answer
1k views

Simple open-source Quantum chemistry or DFT code in C/C++

I know lot of density functional packages in fortran, including one which we are developing in our group (Fireball-DFT) but I don't like fortran very much and I would like something which is easier ...
0
votes
1answer
129 views

How to deal with very low numerical values in C?

I have to work with values such as 1e-15 in my code but I can't. Indeed, because of low precision these values are equivalent to 0. Any ideas?
0
votes
1answer
168 views

Decrease execution time using openMP

I have this method which computes the Fibonacci function: ...
1
vote
0answers
73 views

Problem in analyzing the program of Gauss Jordan Inverse problem

I had to code a program which calculates Inverse of a matrix by Gauss-Jordan Inverse method , I was trying to analyse the program and then code it myself. the link http://hullooo.blogspot.in/2011/...
1
vote
0answers
63 views

Is MATLAB feasible for app deployment versus lower level languages [duplicate]

MATLAB/Octave is a pretty useful language for prototyping scientific computation use cases, however I would like to know if the sheer nature of being a high level language bottlenecks how fast the ...
1
vote
1answer
303 views

Jacobi iteration for finite difference: when to stop?

I implemented a finite difference scheme to solve Poisson's equation in a 2D grid in C. I solve the system by using Jacobi iteration. Everything works fine until I use a while loop to check whether it ...
1
vote
3answers
177 views

MPI in C, all processor run outside of the MPI envir created

I am new to MPI and am trying to figure out the subtleties in it, and for that reason I am just playing around with an easy example. The question I have is that when I run the code below with 2 ...
3
votes
1answer
109 views

Numerical evaluation of the Exponential Integral Ei by rational Chebyshev approximations fails

I am trying to evaluate the Exponential Integral $Ei(x)=-\int^{\infty}_{-x}\frac{e^{-t}}{t}dt$ for $x>0$ (interpreted as the Cauchy principal value) by using rational Chebyshev approximations, ...
0
votes
1answer
127 views

fast adaptive quadrature on equispaced 2-D grid

I need to numerically evaluate 2-D integrals of the form: $$ \mathcal{I}(\theta) = \int_{0}^{1} \int_0^1 \varphi_\theta(x,y) dx dy $$ where $\varphi_\theta$ is a family of smooth functions indexed by ...
0
votes
2answers
107 views

CHOLMOD implementation

I am working on a domain decomposition code in C that uses CHOLMOD to approximate grid values for a PDE in each sub-domain. The issue I have is that the methods use Matrix Market format, which is not ...
0
votes
1answer
150 views

Linear solve using CHLOMOD in C

I am using the open-source CHLOMOD (as here http://faculty.cse.tamu.edu/davis/suitesparse.html) in order to solve a linear system Ax=b (performing A/b=x) in my domain decomposition code but I am ...
0
votes
1answer
150 views

Open Source Linear Algebra Library

I am making a code in C that requires the equivalent of Matlab's '\' command for a linear system of the form AX=B where A is an NxN matrix and X, B are Nx1 vectors- i.e a code that performs X=A\B that ...
-2
votes
2answers
134 views

Array initialization in C

In this bit of code, the X and Y arrays should be identical but for some reason, that I CANNOT figure out for the life of me, X[0] is always 1 rather than 0. I have tried initializing the whole array ...
2
votes
0answers
172 views

Error in MD simulation with Lennard-Jones potential in C, resulting in a lack of conservation of energy

I'm working on a MD simulation using the Lennard-Jones potential and the Velocity Verlet algorithm. The code compiles and runs, but the energy for each time step is not conserved; it decreases ...
2
votes
1answer
321 views

Implementing velocity verlet for harmonic oscillator in C gives error wrt conservation of energy

I'm attempting to implement velocity Verlet with a harmonic oscillator in C, but I have some errors: Energy is not being conserved Energy oscillates much more than I would expect I believe the error ...
1
vote
1answer
132 views

What PRNG function is this?

This is a 16-bit PRNG function, transcribed from assembly to C for easier reading: ...
1
vote
0answers
73 views

PETSc - difference between PetscNew and PetscMalloc

I wonder what is the difference between both functions. In C++, the difference between new and malloc is easier: new allocates memory by calling the constructor. What about PETSc ? In the example, ...
1
vote
1answer
75 views

PETCs - How should one initialize PetscRandom?

The documentation of PETSc shows an example of usage: ...
7
votes
0answers
351 views

Implementing std::nextafter: Should denormals-are-zero mode affect it? If so, how?

This might be the wrong stackexchange site for this question. math.SE, cs.SE, programmers.SE, and of course stackoverflow are all possibilities. I'm hoping to reach an audience that might actually ...
0
votes
1answer
83 views

Indexing Nested Loops in C [closed]

I am having trouble indexing correctly the below statement in C inside a function and then returning it as a pointer. The returning part should not be confusing - hopefully - however the indexing is a ...
1
vote
2answers
192 views

Programming language for HPC [closed]

I'm planning on building a program that will carry out HPC. I'm aware that C/C++ is significantly better than Python in terms of the speed of computation. However, I'm not yet proficient in C/C++, so ...
1
vote
2answers
62 views

Maintain Uniform Distribution across Subranges

Note: this is a continuation of Generate Random Number outside Bounds. I have a function (thanks to the previous question) with the following prototype which returns an integer in the range $[0,b]$, $...
6
votes
3answers
696 views

What do C, C++ and Java have that Fortran 2003 don't? [closed]

As you may know, Fortran is widely and longly (?) used in science. I've heard a lot of people saying that we natural scientists should all migrate to C++ or Java. I've seen people increasingly ...
10
votes
2answers
446 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: ...
6
votes
2answers
235 views

Sum over very small exponentials: Underflow

I am trying to compute (in C) a sum like $S = \sum_i \exp( - a_i )$, where $10^{4} < a_i < 10^{5}$ are approximately normal distributed. So even if I do the Log-Sum-Exp trick $S = \exp(\...
2
votes
2answers
590 views

Kummer's confluent hypergeometric for complex arguments in C/C++?

I need to evaluate Kummer's confluent hypergeometric function for imaginary arguments: $$_1F_1(a,b;ix)$$ where $i$ is the imaginary unit, $a,b,x$ are real, and $a,b>0$. Is there a routine ...
3
votes
2answers
84 views

Do BLAS routines compute their respective operations with minimum error?

Do all BLAS routines compute the respective operation with minimum error ? i.e. Is the reduction in sdot computed with least error ? I need to call these ...
0
votes
1answer
111 views

solver linear system equation

I need to solve to solve a "large" symmetric sparse linear systems, with matrix size 8000? I heard about HSL, ITPACK, but I don't know how to use them, and I am working in C language.
2
votes
1answer
74 views

Use of structs in Axisymmetric Finite Volume method

This might be better somewhere else, but I'll give it a try here first. I'm implementing a finite volume scheme for an axisymmetric problem in C, and am looking for a more efficient way to handle all ...
2
votes
1answer
678 views

Profiling optimized C code using gprof

I have a simple C code with many function calls, which I profiled using gprof. ...
1
vote
1answer
250 views

Kronecker products and basis contractions (ie. B.A.Transpose[B]) in C?

I have implemented a basis transformation in C of the following form kron[A,A]*B*Transpose[kron[A,A]] where A and ...
2
votes
1answer
306 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 ...
4
votes
1answer
835 views

What is wrong with this matrix multiplication?

I am attempting to write a matrix multiplication routine because I need to do some analysis in CUDA and I want to validate it with CPU code. I am trying to use <...
3
votes
2answers
2k views

BLAS, LAPACK or ATLAS for Matrix Multiplication in C

I am trying to find the most optimized way to perform Matrix Multiplication of very large sizes in C language and under Windows 7 or Ubuntu 14.04. And searching led me to BLAS, LAPACK and ATLAS. ...