The tag has no usage guidance.

learn more… | top users | synonyms

1
vote
0answers
29 views

Python DFT library using MPI

I am looking for a discrete Fourier transform (DFT) library that can be run with MPI on Python. Usually, in other language (C, fortran) FFTW is used. There's a Python wrapper for FFTW called pyFFTW, ...
3
votes
0answers
39 views

Solving a 3D (almost radial) convolution with FFT

I have a 3D integral that is almost a radial convolution of the form $$ \int d^{3}k'h(\mathbf{k'})g(|\mathbf{k-k'}|) $$ and I am looking for a fast and efficient algorithm (e.g. FFT) to solve it ...
1
vote
2answers
165 views

C++ libraries for Fast Fourier Transform in high precision

I am looking for a C++ library for Fast Fourier Transform (FFT) in high precision (e.g., using high precision real data types similar to mpfr_t in MPFR or ...
2
votes
0answers
40 views

How to obtain values in physical space for a given spectrum?

My question falls under purview of turbulent flows. I want to add an initial perturbation, for which I have a given energy spectrum (say$ E(k)=ak^4e^{-bk^2} $). The steps involved in getting these ...
2
votes
0answers
39 views

FFT-based Image Rotation Algorithms More Accurate Than Chirp-Z?

We're currently using a Chirp-Z based implementation (Tong and Cox, 1999) for rotation of astronomical images. I was wondering if there were any algorithms/implementations out there that could also be ...
3
votes
1answer
189 views

computing turbulent energy spectrum from isotropic turbulence flow field in a box

I have my 3 dimensional velocity flow-field u, v and w at a given instant of time from DNS using pseudo-spectral method. I need to calculate the energy spectrum ( in Fourier space ) as a function of ...
0
votes
0answers
64 views

Laplace Operator with PyNFFT

I am learning to use PyNFFT for nonuniform FFT. I try to apply the laplace operator to functions. As a test, I want to take $f(x) = \cos( 2\pi i k \cdot x)$, calcualte (using the package) $\Delta f$ ...
4
votes
1answer
86 views

Computing Fourier representation of space dependent advection operator via FFT

Consider the following equation on the circle: $$\dfrac{\partial p(x,t)}{\partial t} = a(x)\dfrac{\partial p(x,t)}{\partial x} \equiv L(p) \enspace ,$$ where $L$ is the operator acting on $p(x,t)$. ...
3
votes
0answers
44 views

Broadening spectral data by using FFT's

I obtain numerical discrete data of the form $$ S_{raw}(\omega) = \sum_{j}w_{j} \delta(\omega-\omega_{j}) $$ to compare the result with experimental data the delta peaks need to be broadened ...
1
vote
0answers
172 views

radially averaged power spectrum of a binary image does not look like power law

It has been known that Fourier power spectrum somehow obeys power law therefore the slope of the spectrum can be used to calculate the fractal dimension of an image. Many people have used it for ...
2
votes
1answer
137 views

precision loss in non-trigonometric, periodic functions using FFTW and NaNs after marching forward in time (Fortran)

I have developed a pseudospectral solver of the Navier-Stokes equations using FFTW. I tested my formulation of right hand sides (RHS) of the NS equations against standard trigonometric functions (...
0
votes
0answers
106 views

FFT parallel processing in MPI

I am working now in Beowulf Cluster and parallel processing, I want code for Fast Fourier transfer functions written in any language, e.g., C/C++. Without using FFTW library based on message passing ...
1
vote
1answer
337 views

Time array from frequency array in FFT using Python

I have done a Fourier transformation of two signals (in time) $S_1(t),S_2(t)$ using numpy's fft which will give me $S_1(f),S_2(f)$. The corresponding frequency grid ...
0
votes
1answer
53 views

Which version of FFTW

At the moment, I'm installing the "GADGET-2" application. In its documentation it says "Note that the MPI-capable version 2.x of FFTW is required, the new version 3 lacks MPI capability at this point. ...
1
vote
1answer
206 views

DST using FFT routine

Please can you help me with my problem? On Wikipedia, in article Discrete sine transform, this is written (chapter Computation): "Although the direct application of these formulas would require O(N2) ...
1
vote
2answers
75 views

A function as a sum of serie of modified FFT coeff. of another function - multiplied by sum number

I solve such a problem. Lets have a function $Y=\sum_{k=-\infty}^\infty i\hat Y e^{ik\pi y}$ and then I have a function which is defined as $X=\sum_{k=-\infty}^\infty ik^2\hat Y e^{ik\pi y}$. I ...
6
votes
1answer
1k views

MPI-based Implementations of FFT

In a numerical computation, I am required to take a multi-dimensional FFT on a distributed-memory cluster. The data is currently distributed using a distributed array in PETSc (DMDA). I initial ...
0
votes
0answers
126 views

FFT - function only in sine series? Can be done with MKL / Lapack?

please can I ask, how one can make from function sine series (Fourier transform) with MKL? I can do "normal" exponential FFT with MKL (Lapack of course), how can I say that I want only sine series? ...
1
vote
1answer
146 views

Discrete convolution

please can I ask a bit stupid question? Let say I need to solve an equation in a form $\frac{\partial X}{\partial t}=\sum_k M_k * X_{n-k}$ How can I do the discrete convolution numerically? I will say ...
10
votes
1answer
1k views

Fast (approximate) evaluation of Chebyshev polynomial

Is there a preferred way how to implement a fast (approximate) evaluation of the Chebyshev interpolation polynomial on uniform grid (given the function values at the Chebyshev nodes)? My problem is ...
12
votes
4answers
637 views

Scalability of Fast Fourier Transform (FFT)

To use the Fast Fourier Transform (FFT) on uniformly sampled data, e.g. in connection with PDE solvers, it is well known that the FFT is an $\mathcal{O}(n\log(n)$) algorithm. How well do the FFT scale ...
6
votes
1answer
359 views

How can I tell VASP 5.2 is compiled with FFTW3?

When VASP 5 was released, the performance was mostly slower than our make of VASP 4.6. I wrote it off as an optimization issue, and went on in my life. Then, in VASP 5.2, with the release notes, I ...