0
votes
0answers
20 views

pFourier Transform using symbolic toolbox

Hi i need to use the symbolic toolbox from matlab and solve the following by fourier transform: $\int^{\infty}_{-\infty}\frac{\sin(at)\sin(bt)}{t^2}dt\text{ }\text{}\text{}$ So far the algo i came ...
0
votes
1answer
22 views

Top and bottom power spectral density of a height profile

Imagine I have a simple 1D height profile which is NOT symmetric. Now, what is truly important for me is to know what are the frequency content of the top profile (i.e. a cut profile above the ...
1
vote
1answer
33 views

Relative error when computing derivatives via FFT

I want to compute a discrete derivative via the FFT. This amounts to multiplication by the wave number in Fourier space, as detailed in the stack exchange answer here. When I increase the ...
0
votes
0answers
17 views

Get a set of points from Fourier plot on Matlab?

I have a program that collects raw data and also does a Fourier transform to get complex numbers. When I feed the raw data into Matlab to do its own FFT, I can get a nice plot of power on frequency. ...
2
votes
1answer
46 views

Fourier series of oscillation in form $\cos(2 \pi \frac{k}{T}+\phi)$

I would like to calculate the fourier coefficients of $\cos(2 \pi \frac{k}{T}+\phi)$ where $T \in \mathbb{N}$ is the period and is arbitrary but fixed, $k \in [1, N-1]$ is the number of oscillations ...
3
votes
1answer
49 views

Image Reconstruction:Phase vs. Magnitude

Figure 1.(c) shows the Test image reconstructed from MAGNITUDE spectrum only. We can say that the intensity values of LOW frequency pixels are comparatively more than HIGH frequency pixels. $$ ...
1
vote
1answer
39 views

How can we represent an image using basis images?

I have read that using Fourier transformation we can decompose any arbitrary image into orthogonal basis images and reconstruct it back. But i don't understand terms like "orthogonal " and "basis ...
0
votes
1answer
101 views

MATLAB: Plotting the inverse Fourier transform of a rectangular pulse.

I'm trying to repeat the results in the image below without using the rectangularPulse(a,b,z) function: Here is my unsuccessful attempt: Here is the code I used to create the first image: ...
1
vote
2answers
35 views

trigonometric interpolation of a sampled signal

Given N sampled points, using the FFT we can get the Fourier transform of those N points $X_k$. With N/2 the Nyquist frequency and $X_0$ the DC value. Using the inverse we can then get back the ...
0
votes
0answers
23 views

trigonometric polynomial using FFT

I am trying to use the FFT to approximate a given function. So i have 10 points xk that are given for example, if i use the FFT that will give me Xk. So now using the inverse FFT we can get the ...
1
vote
3answers
93 views

Calculating own dft via matlab?

We are asked to code our own dft function from the formula : If everything is done correctly it should give the same result with matlab's own dft function, in the end I'm comparing them but they ...
2
votes
0answers
65 views

(newbie) spectral derivative

I have data that form a scalar field on a 2D grid, evenly spaced. The grid has a finite size. There is no particular periodicity patern in my data. I want to calculate the value of the gradient at ...
1
vote
1answer
489 views

Derivative of function using discrete fourier transform (MATLAB)

I'm trying to find the derivative of a function $f(t)$ using the discrete fourier transform. My end goal is to do so numerically, but I suppose if I have the theory down then the rest should follow ...
0
votes
0answers
86 views

The function of fftn in Matlab

Suppose there is a 3 dimension matirx. ...
0
votes
1answer
28 views

Can I use fft of Matlab in this case?

fft is a function for Fast Fourier transform. In Matlab help document, Y=fft(x), $\rightarrow$ $X(k)=\sum\limits_{j=1}^Nx(j)w_N^{(j-1)(k-1)}$ where $w_N=e^{(-2\pi i/N)}$ and $N$ is the length of $x$. ...
0
votes
0answers
49 views

A numerical inverse Fourier transform

I am doing an research in phase noise, And I'm troubled in a paper. In that paper,it says when perform a inverse Fourier transform on ...
2
votes
2answers
1k views

Understanding Fourier transform example in Matlab

I'm studying about Fourier series and transform and I get confused with the following Matlab example of Fourier transformation: ...
0
votes
1answer
46 views

spectral structure of sinusoidal model

let us consider following code ...
1
vote
1answer
86 views

Shifting using fouriertransform

I'm doing a small mathematical exercise where I take a function, perform a Fourier transform on it and then multiply the result by $e^{i\alpha w}$. And then take the inverse Fourier transform of the ...
0
votes
2answers
72 views

Using a function in Matlab

Very new to MATLAB and Im trying to use the FFT function. I got a video which showed me that a function and a normal m file is needed. Created that but now dont know how to call the function from the ...
2
votes
0answers
113 views

Solution of an implicit Fourier transform equation

How does one solve the following equation ($\hat{a}(k)$ denotes the Fourier transform of $a(x)$ and $q$ is real positive): $$\hat{a}(k)=f(k)\widehat{a^q}(k).$$ This equation appeared in some paper. ...
1
vote
1answer
475 views

reducing amplitude of fft spectrum with constant phase

I have a time series that I converted to the frequency domain using fft in matlab. I want to reduce the amplitude at a given frequency range (remove a peak between 1.5 and 2Hz) but keep the phase ...
1
vote
0answers
71 views

Output of wavelet transforms

I am working on a time sensitive computer science and fluid dynamics project that requires me to find applications of wavelet analysis. I know that at its core, a wavelet transform simply takes a ...
0
votes
2answers
394 views

Programming discrete fourier coefficients in matlab

Alright so I am having the following issue: I want to figure out how to find the fourier coefficients of the following function: $$D(X)=\frac {a'(x)} {1+a'(x)^2}$$ Where $a(x)$ is an arbitrary ...
0
votes
1answer
254 views

Fourier Transform for a Convolution

Alright, so I am using the Convolution property of Fourier Transforms to find a function $f(x)$. So the obvious equation: $h(x) = f(x) \ast g(x)$. Definitions: $$g(x)=Rect\left[\frac x w ...
1
vote
0answers
154 views

Convolution property in terms of fft (matlab)

I am working on some signal processing and I have the following data: ...
1
vote
0answers
216 views

Help with Hermitian Symmetry and its inverse Fourier transform in MATLAB.

I have tried to impose Hermitian symmetry on the complex number $z$ which is varies with $x$. I need to take its inverse Fourier transform. A hermitian symmetry should give a real valued inverse FT. ...
-1
votes
2answers
160 views

How to remove high frequncies having fft?

What are the units of measure of FFT elements? Can I just set higher elements to zero to filter out higher frequencies? It looks like no. ...
1
vote
0answers
56 views

Help in implementing of peak function in Fourier transform

I have a function Peak function I know how to implement it in time range just need to caclulate $r$. first I initial $x$, y with a range and meshgrid them, after it calculate $r$ ...
1
vote
1answer
352 views

Discretization of differential equation via FFT routine

I just have a question related to the following problem: Find a discrete approximation to the differential equation $u^{\prime \prime} + 2u^{\prime} + 2u = 3\cos(6t)$ using Equation 3.12 for these ...
3
votes
1answer
462 views

MatLab - Fast Fourier Transform

I have just started messing around with the fft function in MatLab, but can't quite understand the output. Say I write the following: ...
2
votes
0answers
226 views

FFT in MATLAB is shifted in frequency [closed]

I have a signal in MATLAB on which I'd like to perform an FFT. My signal is stored in s, and I use the code below (inspired by the MATLAB help): ...
2
votes
1answer
647 views

Matlab FFT-algorithm example, one simple question

This is a question about an example for the software Matlab, but I still chose to ask it here, since I suspect that the question is more about the math involved than the software itself. I want to ...
3
votes
1answer
678 views

Normalizing scilab's FFT

I want to normalize the FFT used in scilab in a way so that the absolute values of the coefficients equal to the amplitudes of the time domain signal with that frequency. Example: I want an input ...
2
votes
0answers
407 views

Understanding Fourier Transform and FFT

First off, I'm sorry if this is a repost. I am currently writing my thesis, and I've been thrown into some Fourier analysis, which I know nothing of. So, even if this question has been posted before, ...
1
vote
0answers
158 views

how to correctly implement my own version of fft in matlab?

Currently I'm developing my own version of fft/ifft on matlab (homework) based on algorithm of Cooley/Tukey (radix 2). My code works fine for zero-padding images, but, how can I handle non-zero ...
1
vote
3answers
8k views

square wave matlab code

I'm having some trouble generating a square wave in matlab via my equation. Just wondering if anyone has some insight on what I am missing here in my code? I was thinking I could easily generate a ...
1
vote
1answer
266 views

Representation of Fourier Transform's vectors

I am just learning FFTs and I am trying to debug a problem in MATLAB. I think I don't understand how is MATLAB's FFT function handling the polynomial powers, or I am doing something wrong manually. ...
0
votes
1answer
3k views

Rebuilding original signal from frequencies, amplitude, and phase obtained after doing an fft

Rebuilding original signal from frequencies, amplitude, and phase obtained after doing an fft. Greetings I'm trying to rebuild a signal from the frequency, amplitude, and phase obtained after I do ...
1
vote
1answer
615 views

How can I increase/decrease (frequency/pitch) and phase using fft/ifft

How can I increase/decrease (frequency/pitch) and phase using fft/ifft I think I have the basic code but I’m not sure what to do next PS: It's done in Octave/matlab code Example I have a signal that ...
2
votes
1answer
188 views

FFT and changing frequency and vectorizing FOR loop

I can increase and decrease the frequency of a signal using the combination of fft and a Fourier series expansion FOR loop in the code below but if the signal/array is to large it becomes extremely ...
0
votes
1answer
2k views

editing signal in frequency domain and converting back to time domain

editing signal in frequency domain and converting back to time domain the code is matlab / open source octave code Greetings All I would like to be able to edit different aspects of a signal ...