## Forums Search for: FFTW

## fftw comiling error

inGood Day, I have been trying to compile fftw on my linux computer but I get error. code is; #include int main() { int...

Good Day, I have been trying to compile fftw on my linux computer but I get error. code is; #include int main() { int N=28; fftw_complex in[N], out[N]; fftw_plan p; p = fftw_create_plan(N, FFTW_FORWARD, FFTW_ESTIMATE); fftw_one(p, in, out); fftw_destroy_plan(p); } error messege:: > > linux:~ # gcc -lfftw3 -o fft

## FFTW + low pass filtering + reverse FFTW

inDear FFTW experts, I'm using 2d r2c fftw on images, and now I would like to do a low pass filtering. I compute the...

Dear FFTW experts, I'm using 2d r2c fftw on images, and now I would like to do a low pass filtering. I compute the module (sqrt(realpart*realpart+imagpart*imagpart)) of my data, and if it exceeds a threshold, I set it to zero. Therefore, I get an array of real data, and I don't know if I can use c2r transform by fulfilling my fftw_complex array with my data (e. g. I put the value in the real pa...

## fftw bench assessment

For starters apologies in advance if I'm in in the wrong NG. Downloaded fftw and I'm trying to get an assessment on the output surround the...

For starters apologies in advance if I'm in in the wrong NG. Downloaded fftw and I'm trying to get an assessment on the output surround the command 'bench -sib246'. On my machine this outputs: C:\dev\vc++_2008\fft\fftw> lib /def:libfftw3-3.def 'lib' is not recognized as an internal or external command, operable program or batch file. C:\dev\vc++_2008\fft\fftw> bench -s option -s requ

## FFTW?

inHello, can anyone explain me how to perform the convolution of two dimentional array with fftw? Thanks

Hello, can anyone explain me how to perform the convolution of two dimentional array with fftw? Thanks

## FFTW 3.3-beta1 available

Dear DSP and numerics folks, You might be interested to know that a beta release of FFTW 3.3 is now available from www.fftw.org, with the...

Dear DSP and numerics folks, You might be interested to know that a beta release of FFTW 3.3 is now available from www.fftw.org, with the final 3.3 release scheduled for July 25. This release includes several major new features, including support for 256-bit AVX instructions on recent Intel/AMD processors and an MPI parallel interface. Regards, Steven G. Johnson Matteo Frigo

## FFTW multi-threaded routines, what's use case for them?

inI'm creating a web application that accepts client requests to crunch math on a server. The application will receive multiple client...

I'm creating a web application that accepts client requests to crunch math on a server. The application will receive multiple client requests simultaneously. Was FFTW's multi-threaded routines intended to: (A) process all client requests serially through FFTW, but for the current client process being executed by FFTW, have it use multiple cores (e.g. threads) to increase speed of execution for ...

## Calling FFTW from C++? (x-posted)

inHi, I am currently working on a program using FFTW-> http://www.fftw.org . My basic C program to compute the 2D Fourier transform of a bunch...

Hi, I am currently working on a program using FFTW-> http://www.fftw.org . My basic C program to compute the 2D Fourier transform of a bunch of data works fine when I compile it with gcc. However, I would like to incorporate that code into a larger program that I wrote with C++. Unfortunately, I cannot get my program to compile with g++. I compile it as follows: g++ ft2d.c -o ft2d -I

## does FFTW break when subjected to multiple simultaneous requests?

inAnyone know if multiple simultaneous requests to (the same instance of) FFTW are made, will FFTW either: (1) simply serialize these requests...

Anyone know if multiple simultaneous requests to (the same instance of) FFTW are made, will FFTW either: (1) simply serialize these requests (e.g. perform one right after the other), thereby completing all requests given sufficient time, or (2) crash or otherwise be unhappy? If (1) occurs, then all is well. But if (2) occurs, then I need to manage the requests into a queue and make sure F...

## Partial Derivative for 3D function by FFTW

inDear FFTW experts, I want to do the partial derivative for a 3D function by FFTW. For example, I have a 3D function P(x,y,z), and I want to...

Dear FFTW experts, I want to do the partial derivative for a 3D function by FFTW. For example, I have a 3D function P(x,y,z), and I want to compute dP/dx and dP/dy (I can not find the symbol for partial so I use "d" here). As I remembered: 1. Determine dP/dx:(P is a 3D data) (1)I should do fourier transfrom of P(x,y,z) with x direction(1D transform for 3D data) (2)multiply with i*Wx (3)i...

## FFTW small difference for r2c ?

Hello, I am using FFTW v3.2 in C++ to compute the 3d DFT of a real image. I use the FFT as part of an iterative algorithm in which high...

Hello, I am using FFTW v3.2 in C++ to compute the 3d DFT of a real image. I use the FFT as part of an iterative algorithm in which high accuracy is a must, so I checked the outputs of the FFTW and found some very small difference depending on whether I used the r2c or not. By small difference I mean about a 17% increase in numerical error versus by the traditional error. In pseudo-code, if...

## benchmarking advanced interface using fftw bench

Hi, I would like to use the fftw bench program to time the following. Use plan_many_dft from Advanced interface to calculate a bunch of ffts...

Hi, I would like to use the fftw bench program to time the following. Use plan_many_dft from Advanced interface to calculate a bunch of ffts on a contiguous array of complex numbers. Can some one help me with the options i need to pass on to fftw bench program to be able to choose plan_many option. I the readme file, suggestions for inplace and out of place 2d fft examples are shown. Apparent...

## FFTW speed !!

inGood morning, I'm using FFTW library for my project. I'm working on a PowerPC 7447 processor with vxWorks operating system. I have generated...

Good morning, I'm using FFTW library for my project. I'm working on a PowerPC 7447 processor with vxWorks operating system. I have generated fftw library through gcc 2.95 compiler using the sequent options for obj files: -O3 -fomit-frame-pointer -fstrict-aliasing -fvec-eabi -mcpu=7450 I'm working in single precision. My problem is the speed of fft elaboration. I'm using the BASIC interfa...

## trouble calculating the laplacian of a function using fftw's dct function

Hello, I am having a lot of trouble computing the Laplacian of a function (with neumann boundary conditions) using fftw's DCT function. I...

Hello, I am having a lot of trouble computing the Laplacian of a function (with neumann boundary conditions) using fftw's DCT function. I do this by taking the cosine transform using fftw, multiplying it by -k^2 (negative wave vectors squared), back transforming, and normalizing. Here is my fortran code. Sorry that its a bit messy. It seems to work when the periodic extention of the fu...

## Is the output of FFTW in angular velocity domain?

Hi, I have a question in FFTW, I need to make the out put data in angular velocity domain, like 1/2*sqrt(pi)*exp(omiga**2/4) for exp(-x**2). I...

Hi, I have a question in FFTW, I need to make the out put data in angular velocity domain, like 1/2*sqrt(pi)*exp(omiga**2/4) for exp(-x**2). I guess the FFTW output is in frequency domain, what do I need to do to change it? Thanks, Shuangyi

## Using FFTW 3 DLL w/ CLR

in(This post regards compiling and linking to the FFTW library on Windows. Apologies if this is off-topic here.) I'm attempting to link an...

(This post regards compiling and linking to the FFTW library on Windows. Apologies if this is off-topic here.) I'm attempting to link an application to the FFTW .lib and .dll. I can build and run a raw c++ sample application perfectly, as follows: // testapp.cpp #include "fftw3.h" int main() { const unsigned int INPUT_SIZE 100; double* input = (double*)fftw_malloc(sizeof(double)...

## Convolution and FFTW question.

inSeems dumb*, but what the hey: (data sets are 1D PCM audio data) Convolution is O(n*m) where n is the length of one vector to be convolved, m...

Seems dumb*, but what the hey: (data sets are 1D PCM audio data) Convolution is O(n*m) where n is the length of one vector to be convolved, m is the length of the other vector. Convolution using FFT is alleged to be O(n log(n))... *part of this is things I can't easily find in the FFTW docs. 1) The product of a DFT from FFTW is of the same length as the original PCM stream to which th...

## FFTW Accuracy vs Matlab Accuracy

inHi, i'm using FFTW to computer determine the SNR of a recorded sinusoidal signal. (1khz sinus for 5seconds @ 48khz) I'm experiencing a...

Hi, i'm using FFTW to computer determine the SNR of a recorded sinusoidal signal. (1khz sinus for 5seconds @ 48khz) I'm experiencing a strange behaviour: if i compute the fft with FFTW i obtain really different values from what matlab compute. To be more specific: i compute a real 2 real fft with: ApplyWindow(BLACKMANHARRIS);//

## Complex Multiplication and convolution with FFTW

inHi! I am currently use FFTW to compute a two dimentional DFT of real data, I readed the FFTW documentation an proced as follow: /*** The fft.h...

Hi! I am currently use FFTW to compute a two dimentional DFT of real data, I readed the FFTW documentation an proced as follow: /*** The fft.h file *** #include using namespace std; class fft { public: fft(); fft(int rows, int cols); ~fft(); fftw_complex * forward(double *); double * backward(fftw_complex *); fftw_complex * multiply(fftw_complex *, fftw_c

## IFFT conversion using FFTW libraries

inHi, I am trying to convert a FFT and IFFT Matlab code to C using the fftw libraries. Hoiwever, I am stuck at a particular step: The Matlab...

Hi, I am trying to convert a FFT and IFFT Matlab code to C using the fftw libraries. Hoiwever, I am stuck at a particular step: The Matlab command is: G = ifftn(P21,'symmetric'); ow do I convert this statement to C using the fftw library. I have tried the following steps: 1.I used fftw_plan_dft_2d to compute the FFT for a double array of size nx by ny. the FFT values match the Matlab values. I...

## Matlab and VC++ values differ when determining FFTusing FFTW

inHi there, I have recently started using FFTW to determine fft in C++, so I am really not good at it. I am currently trying to just evaluate my...

Hi there, I have recently started using FFTW to determine fft in C++, so I am really not good at it. I am currently trying to just evaluate my fft values in both matlab and C++. I have used FFTW to determine the fft in C++ and fft2 in matlab for a 4*4 matrix [int values]. My values were same in both Matlab and C++. My real requirement is to use fft on complex matrices. But my values no longer m...