Displaying 20 results from an estimated 10000 matches similar to: "R fft on 2D matrix"
2001 Sep 24
1
2D fft DC shift
Hi Everyone,
Does anyone know how to take the output of a 2D fft()
and shift the DC component to the center? Is there a
function that does that?
if you know, please send me an email.
thanks for any help!
brad
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2009 Nov 28
2
fft and filtering puzzle
I am puzzled by a filtering problem using fft(). I don't blame R.
I have a waveform y consisting of the sum of 2 sinewaves having freqs f1 and f2.
I do s = fft() of y.
Remove s's spike at freq=f2
Do inverse fft on s.
The resulting waveform still has a lot of f2 in it! But the filtering
should have removed it all.
What is going on, and how to fix??
Thanks very much for any help.
Bill
2008 Apr 30
2
fft: characteristic function to distribution
The characteristic function is the inverse Fourier transform of the
distribution function. The characteristic function of a normaly
distributed random variable is exp(-t^2/2).
x=seq(-2,2,length=100)
fft(pnorm(x),inverse=T)/length(x)
exp(-x^2/2)
Why aren't the inverse fft and the mentioned function the same?
Thanks for help,
Thomas
2008 Sep 30
1
fft inverse display help
I have a a simple function that generates a time series square wave:
genseq <- function()
{
x <- numeric(4*365)
s <- seq(as.Date("2005-01-01"), as.Date("2008-12-31"), by="month")
ob <- as.vector(s[c(10,22,34,46)] - as.Date("2005-01-01"))
oe <- as.vector(s[c(11,23,35,47)] - as.Date("2005-01-01"))
for(.index in 1:length(ob))
2010 May 30
1
Calling fft from C
Hi
I have made a R function 'convolve2' for convolution of two real
valued vectors based on Rs 'convolve' with option type="open" - see
below.
(exp.length and irf.length are variables set in another part of the program)
I wish to implement the function convolve2 in C and use it in a
function used from R with .Call - e.g. I need to call fft in C.
All I can find in the
2005 Nov 03
1
Real FFT
The book "Numerical Recipes in Fortran77" by Press, Teukolsky, Vetterling and Flannery describes a way to "pack" the even and odd coordinates of a real vector "R" into a complex vector "C" of half the length. Then using various FFT symmetries, they extract the FFT of "R" from the FFT of "C" which is half the length of "R",
1997 Dec 11
1
R-alpha: fft does not act as described in help(fft)
Hello!
thank you for your efforts creating R!
While preparing the next lessons I found that I had
to multiply with 1/length(x) by hand if I want to
get the inverse Fouriertransform.
The help states it will do it by itself.
Version R-0.60.1, Linux
Seems to be pretty easy to correct either the fft or :-) the help(fft)!
Cu Detlef
Detlef Steuer Universitaet Dortmund ///////
2003 Mar 11
3
fft help
Hi R-users:
I want to know if there is an easy way to obtain a Fourier Transform form
a vector or an array (just like fft does), but with a more density base.
I mean, if I have a vector of 512 of length, I want the Fourier
Transform to
be 1024, or 2048, etc, in length (de u domain). Or should I modify the
fft C code to do that?
If I want to modify the precision of the fft function, which
2008 Sep 04
1
Plotting the complex fft in 3D?
Hello,
I'm new to R (using it since about two weeks),
but absolutely a fan of it from the beginning on. :-)
Best tool for working with data I found. :-)
I tried using the fft() and other funcitons for
analysing time series.
What I would be glad to have, would be a
convenient way to display the complex result
of a fft in a way, that real and imaginary parts
each use an axis for themselves,
2008 Oct 27
2
Stuck with FFT
Dear all,
Before I can get into serious Fourier analysis of Radon time-series I am
practising with 24hour and 24.8hour sinusoids to assist with my
interpretation of signals ittributed to tidal input to Radon time series.
I am stuck. I have tried researching this to no avail. I am awating a book
that should describe fourier transforms in detail and another one that
should discuss the R
2006 Jul 30
1
Parametric links for glm?
At useR 2006 I mentioned that it would be nice to have a way to
specify binomial links
that involved free parameters and described some experience with a
Gosset link involving
a free degrees of freedom parameter, and a Tukey-lambda link with two
free parameters.
My implementation of this involved some rather kludgey modifications
of binomial,
make.link and glm that (essentially) added a
2002 Apr 01
1
fft fails for lengths 392, 588, 968, 980 .... (PR#1429)
R 1.4.1, Linux and Windows
for(i in 1:1000) {
X <- rnorm(i)
XX <- fft(fft(X), inverse=T)/i
if(max(Mod(XX-X)) > 1e-10) print(i)
}
[1] 392
[1] 588
[1] 968
[1] 980
and I then get a segfault during gc(). The answers are way off, with
imaginary parts 1e10 or more.
These numbers are all multiples of 7^2 or 11^2.
(Based on a report to R-help
Date: Thu, 28 Mar 2002 09:37:34
2007 Jan 23
1
AEC FFT replacement for TI 55x
I am in the process of dropping the TI DSP lib fft routines into the AEC.
Currently, FFTWrap.c uses the USE_SMALLFT and USE_KISS_FFT to select between
two packages of FFT routines. ]
#ifdef USE_SMALLFT
...
#elif defined(USE_KISS_FFT)
...
#else
#error No other FFT implemented
#endif
My guess is that every DSP and many other processors will have their own
specific FFT and iFFT. What method
2003 Jan 09
1
fft(x, inv=TRUE)
I started out with a real vector b and then obtained its Fourier transform
thus
B<-fft(b)
When I did
F<-fft(B, inv=TRUE)
I expected that F would be the inverse FT of B but it still has imaginary
components.
Should the inverse FT not be purely real? Am I missing something?
Thanks,
Peter.
2013 Jul 16
1
Query regarding FFT in Opus
Dear Experts,
I want to know if the KISS FFT in opus can be replaced with fast FFT. What
are the implications & things to be taken care if this is done.
Also, I saw in FFT code comments that in-line FFT not supported. Please let
me know the reason for this.
Thanks in advance.
Regards,
Mahantesh
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2014 Dec 24
6
[RFC][FFT][Fixed-Point][NEON] NEON-Optimize Fixed-Point FFT?
Hi,
I am working on DSP module of Ne10. I see there are fixed-point and floating-point FFT inside Opus. Is fixed-point FFT only a fall back for CPU without VFP? On ARMv7-A and ARMv8-A, benchmark result shows that fixed-point (int32) and floating-point (float32) FFT have similar performance. I guess fixed-point version is not often used on these platforms. Is it worth the effort to NEON-optimize
2015 Apr 30
3
[RFC PATCH v1 0/8] Ne10 fft fixed and previous
On 29 April 2015 at 17:22, Timothy B. Terriberry <tterribe at xiph.org> wrote:
>
> Viswanath Puttagunta wrote:
>>
>> This patch series is follow up on work I posted on [1].
>> In addition to what was posted on [1], this patch series mainly
>> integrates Fixed point FFT implementations in NE10 library into opus.
>> You can view my opus wip code at [2].
>
2014 Nov 25
1
[Profiling][FFT][AArch64] FFT Profiling data on AArch64
Hi everyone,
I have profiled Opus on AArch64. I just run opus_demo with some pcm files.
Following is time proportion of FFT with different bitrate.
Bitrate | Time cost by FFT/iFFT
24kb/s | 15%
48kb/s | 15%
96kb/s | 13%
Any comment? I want some data close to real application, any suggestion?
Thanks,
Phil Wang
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2014 Dec 11
2
[ARM][FFT][NEON] Integrate Ne10 into Opus?
Hi everyone,
I am working on Ne10 project. Ne10 provides NEON optimized FFT routines that
are much faster (compared to those without NEON), on most ARMv7-A and all
ARMv8-A devices. How about integrate it into Opus?
I am not familiar with configure script, but I find "Optinal Packages" in
it. If we provides --with-ne10-fft option, the one extra thing that users
need to do is to
2004 Mar 11
5
fft question
Hi!
I am using the fft() function the base package to transform some 1d signal.
If I use this standar fucntion I get a very huge first fourier coeficient.
I think this dues to the handling of the borders of the signal.
Usually in fft especially in image processing the signal is simulated to be continuous by adding the signal several times periodically. My question is, is there some function