Questions tagged [fortran]
Fortran is a general purpose programming language widely used by the scientific computing community.
151
questions
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0answers
65 views
Which code to learn for the “next level” in computation [closed]
I doing very intensive calculation with GNU octave. I plan to write other codes more laborious, so I need a language optimized for numerical computation. Because of performance, I think that a ...
0
votes
2answers
113 views
Parallel output in ASCII-format with MPI
After some parallel computations, I need to write the results in a file and for plotting reasons, I want them in ASCII format. Because of performance issues, I want to avoid to ...
-1
votes
3answers
155 views
Solving coupled ODEs using Runge-Kutta method
I want to solve the following sets of $n$ coupled equations. Initial values of $x_{n}(t)$ and $p_{n}(t)$ are specified.
The problem is, I have an 1D lattice where every particle is bound with ...
2
votes
0answers
53 views
Processing time steps in chunks with Fortran [closed]
My PDE simulation program written in Fortran has to make about 2 million variable time steps. But with each time step it slows down more and more, so that if it initially makes 1000 time steps per ...
2
votes
1answer
83 views
Testing a block tridiagonal system of equations
In 1D problems, tridiagonal systems of equations are obtained when we use finite-difference or finite-volumes in a structured mesh. A wide solver is the TDMA algorithm here. In two-dimensional ...
2
votes
1answer
95 views
What is good practice for protecting parent scope variables in Fortran?
So I just picked up a project that is written in fortran90. I am used to coding in python and C.
What is really troubling for me is the use of subroutines in fortran90. In fortran people use ...
0
votes
1answer
140 views
How to use LAPACK function (DGELSY) in Fortran
I am trying to use Least Squares Minimization to solve a the matrix problem: b = A*x for x. The system is overdetermined, and A is a dense matrix.
In the LAPACK library, I believe the routine DGELSY ...
1
vote
2answers
151 views
Second derivative using Fornberg finite difference method
I have some discrete data, non-equispaced in $x$, $y=f(x)$.
I want to use a numerical finite difference method to calculate the second derivatives of $y$, at some point.
I am using the Fornberg ...
1
vote
1answer
94 views
Gaussian Elimination Using Fortran [closed]
I developed the code below for performing gaussian elimination in order to evaluate the determinant of a matrix:
...
0
votes
1answer
50 views
Access PETSc data in totalview?
Is it possible to view the data stored in the various PETSc data types from within totalview?
Ordinarily, PETSc types are integers which act as pointers to the actual data (obviously my understanding ...
1
vote
1answer
264 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
1answer
306 views
A robust algorithm to sort a non-convex polygon vertices
Let v_{0},...,v_{N-1} be N points in a Cartesian xy plane defining the vertices of closed polygon (i.e. v_{N} = v_{0}).
Let P_{0}...
0
votes
1answer
98 views
Compute outward normal and surface area for 8 noded brick element in FEA
I have a cube which is divided into 8 small cubes by bisecting each edge, I am trying to find out the surface area of each of the faces and the corresponding outward normals for them. This operation ...
1
vote
1answer
279 views
How write a integration loop in fortran, leapfrog scheme to solvind PDE (advection)?
I want to resolve numerically this equation using of difference finite method with Leapfrog Scheme
$$\frac{\partial{u}}{\partial t}+ v \frac{\partial{u}}{\partial x}= 0 $$
I'm trying to write a code ...
4
votes
2answers
114 views
Analytical testing/quality control for scientific software in professional setting
I am charged with maintaining a buildserver on Teamcity which is meant to test our in house FE software. Currently our test suite consists of a list of benchmarks which run every time a commit is made ...
4
votes
1answer
148 views
Compute bilinear form with LAPACK
I need to compute a bilinear form for a set of left and right vectors
$$ w_k = \sum_{i,j} V_{ik}^*A_{ij}U_{jk},$$
where $A_{ij}\in\mathbb{R}$ and $U_{jk}, V_{ik} \in \mathbb{C}$ (Assume that all the ...
2
votes
0answers
60 views
Parallel compact schemes using the Parallal Diagonal Dominant (PDD) algorithm
I would like to use the PDD algorithm developed by Sun to solve tridiagonal matrices in parallel for the following compact finite difference scheme:
$
\begin{align}
\dfrac{1}{4}f^{'}_{i-1} + f^{'}_i +...
5
votes
2answers
254 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 ...
0
votes
1answer
932 views
implementation of a simple SPH example
I am currently learning the Smoothed Particle Hydrodynamics method that I need to use later in my thesis. I have studied the mathematics behind the method and I want to code a simple example to show ...
1
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0answers
80 views
Dealing with non-physical negative ODE solutions using ODEPACK
Hi and thank you all again. I am solving the reaction-diffusion-advection equation as follows
$ \partial_{t} n\left(t,z\right) = -\partial_{z}\left(\Phi\left(t,z\right)\right) + p\left(t,z\right) -n\...
0
votes
3answers
324 views
Why there are people that still prefer fortran 77 over new versions?
I am reading some notes from a course in numerical analysis for physical sciences and it is my impression that there are still people that prefer Fortran 77 over new version due to the implicit ...
1
vote
1answer
197 views
Bulirsch-Stoer algorithm to solve simple chemistry. Spanning long time intervals after stationarity
Hi all and thank you in advance.
I am working on a time-dependent transport-chemistry model to study the composition of planetary atmospheres.
The equations are the following
$$\frac{\partial n(z,t)}...
0
votes
1answer
152 views
implicit method (crank-Nicolson) I not understand the procedure [closed]
I'm trying to understand the passage through this equation can be written for easily solved with the fortran alghorithm in particular i don't understood the meaning of L_x and L_xx ... what (-1,0,1) ...
0
votes
1answer
134 views
Parameter identification for first order ODE
I have two arrays $f(z)$ and $z$ both indexed by k and I want to solve $\frac{df}{dz}=\mu(1-f)$ to find $\mu(z)$
What would be the best numerical method to solve this equation?
5
votes
1answer
1k views
Loop optimization with f2py, Cython and Numba
I tried to used f2py, Cython and Numba to make a simple loop structure be faster in python. Python implementation:
...
1
vote
1answer
174 views
LAPACK: ZGETRF with INFO greater than zero but ZGETRI does not fail.
I am computing the inverse of a complex matrix. I execute ZGETRF but U(2,2) = 0. When I compute ZGETRI, the inverse is determined. Can I trust this inverse?
5
votes
1answer
474 views
Half precision in Fortran
To improve the time efficiency of my code, I'd like to test a lower precision for real number, using e.g. half precision (2 bytes).
However, I'm not sure if I can do that in Fortran.
After playing ...
4
votes
5answers
3k views
What is the difference between MATLAB and FORTRAN?
In our university some Ph.D students for computational methods prefer FORTRAN over MATLAB. I can't understand why? What is the difference between them when are used in computational methods like ...
1
vote
0answers
543 views
IDE for Scientific computing using Fortran [closed]
I am looking to learn Fortran for Scientific Computing, which IDE setup for this exists that supports debugging, code completion capabilities and offers granular Running time Analytics. I am ...
1
vote
0answers
66 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
237 views
Numerical Free Fall Analysis with RK4
I am trying to calculate real speed and time in free fall of a body. I wrote a code in Fortran and I am trying to improve it by using RK4 method
x=time y=total free fall
Purple line using:
...
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vote
0answers
112 views
Computing only the $k$ biggest eigenvalues and eigenvectors with Scalapack
Given that there are eigensolvers in Scalapack that use a divide and conquer method, is there any way we can use Scalapack functions to only compute the first $k$ dominant eigenvalues and ...
1
vote
1answer
85 views
Declare variable to substitute one calculate only once
Frame of the question
I am currently editing an add-on module to an ocean/circulation model, which is written in Fortran. The code of the main model is quite optimized with respect to short run time (...
0
votes
1answer
649 views
Best books and notes for beginners in the parallel FORTRAN 90 programming
I am a PhD student and my field of study is Quantum Information and Computation in the theoretical aspect. Actually I write the computer codes/program in FORTRAN 90 which are serial codes but now I ...
1
vote
0answers
177 views
Mass conservation in atmospheric continuity equation numerical solution
My phd project is heavily related to numerical modeling of planetary atmospheres. In particular now I am dealing with a particular expression of the continuity equation, involving a thermodynamic flux....
0
votes
1answer
149 views
checksum of a distributed variable
Let say I have N computers and 2 N-by-N matrices distributed across them called A and B. Matrix A is row distributed while B is column distributed. Therefore, processor i knows
...
2
votes
0answers
279 views
Algorithm for face based data-structure - CFD
Good morning
I'm trying to develop an unstructured CFD code to solve Euler equations in a finite-volume (cell-centered) context (learning purposes). I was able to build from a cgns file some basic ...
1
vote
2answers
251 views
derivative of an array
Hi I am trying to take a derivative of an array but am having trouble. The array is two dimensional, $x$ and $y$ directions. I would like to take a derivative along $x$ and along $y$ using central ...
0
votes
2answers
284 views
Using two computers to run one parallelized program with intel fortran [closed]
I have two computers, both with 4-cores and I am running some heavy computational stuff in one of them using Intel Parallel Studio Cluster edition. I am coding in fortran and making extensive use of ...
3
votes
1answer
118 views
Alternative to messy grid node indexing within multiple layers of loops
Recently,I dive into a set of somehow ancient Fortran codes and try to fully understand them. A large fraction of these codes are multiple layers of loops over many state variable dimensions, which ...
0
votes
1answer
82 views
0 Hz (quite sharp) peak in FFT and division by 0
In a previous question, link, I asked about how I could most effectively do a Fourier Transform of a radial function given at certain values and which we knew the asymptotical behaviour of. The ...
1
vote
1answer
277 views
Does anyone have a driver for fortran DAE solver - COLDAE?
Coldae is a solver writter by U Ascher and R Spiteri, located here http://www.cs.ubc.ca/~ascher/coldae.f .
It can solve upto index-2 DAEs using collocation.
I am new to Fortran, and having a hard ...
3
votes
2answers
328 views
How to calculate efficiently and accurately the Fourier transform of a radial function in Fortran
As my question states, I want to calculate the Fourier transform $F(q)$ of a radial function $f(r)$ (defined on $[0,\infty)$ and which decays like an exponential $\exp(-Ar+b)$ at large $r$) as ...
1
vote
1answer
198 views
A fast I/O file format readable by Fortran, Java, PHP?
I am writing a Fortran program that does fairly light weigt computation on fairly large data files. The output must be readable by some Java-script (that i have no insight in) and preferably also by ...
0
votes
1answer
507 views
Fortran round-off error with floating point operations
I have simple code, which flags nodes with in region enclosed by cylinder. On implementing the code, the result is mild tilt of the cylinder observed case with $\theta=90^{\circ}$.
The algorithm for ...
3
votes
1answer
3k views
How do I program periodic boundary conditions? [duplicate]
Hi I have a code below that solves non linear coupled PDE's given Dirichlet boundary conditions. However I need to implement periodic boundary conditions. The periodic boundary conditions are ...
1
vote
0answers
654 views
Generating Random Numbers in Fortran for Metropolis method
I am having a really hard time getting any kind of reliable / consistent result from my Metropolis code. I have torn it apart and am now examining just the randomness in my random number generator.
I ...
1
vote
0answers
644 views
Heat equation from implicit scheme with Neumann B.C
To solve the heat equation from implicit scheme subject to Neumann boundary condition we can write:
$$
T_i^{j+1}-T_i^{j}=\alpha (T_{i+1}^{j+1}-2T_{i}^{j+1}+T_{i-1}^{j+1})
$$
$$
\textbf{A} T^{n+1} = T^...
6
votes
1answer
165 views
How to compare runtimes of two algorithms in a reproducible way
I am solving one relatively simple problem with two different algorithm: one which uses brute force while the other is optimized. For a variety of reasons I actually cannot show the codes here but I ...
0
votes
2answers
459 views
efficient MPI collective non-blocking communication
I am facing a problem with MPI (Fortran). I have a really big matrix at each node and they differ at different nodes. At some point of my calculations, each node needs the matrix from all other nodes, ...
