Linked Questions

4 votes
1 answer
3k views

Why Fourier transform is symmetric no matter what interval I choose? [duplicate]

I'm solving a vibration problem. After solving two systems of ODEs (one valid in 0-0.1 and the other in 0.1-1) I get the plot of 3 functions, one of them is this, the plot of the variable $y_w$ (Image ...
mtlvc0's user avatar
  • 43
0 votes
1 answer
1k views

Fourier FFT frequencies [duplicate]

I am using FFT (Fourier) on a dataset that contains the temperature along a rod 1m long. The data is sampled with a spacing of <...
BillyJean's user avatar
  • 1,253
1 vote
1 answer
1k views

How to set up the Fourier domain for a Fourier Transform? [duplicate]

I am having trouble understanding how to set up the grid in the Fourier domain, while performing Discrete Fourier Transforms. This might be a very trivial question, but I'd appreciate any help ...
Sandesh's user avatar
  • 11
2 votes
0 answers
150 views

How to do the Fourier transform of a picture? [duplicate]

I want to generate Fourier transforms of a picture. the transform can represent the diffraction pattern of the picture. Basically, if I have a picture. Then, the result should look like this: For a ...
BNHSX's user avatar
  • 929
22 votes
4 answers
21k views

Plotting Fourier spectrum versus frequency of a signal

I have looked around here, and i am sure this has been answered, but i don't understand it. The thing is, I have taken a introductory signal processing course, and we had to use Mathematica, and i had ...
mickey's user avatar
  • 375
14 votes
2 answers
20k views

Plotting the frequency spectrum of a data series using Fourier

testData = Table[N@Sin[500 x], {x, 0, 100}]; ListLinePlot[Abs[Fourier[testData]], PlotRange -> Full] Gives me Which I do not expect because the Fourier ...
C. E.'s user avatar
  • 70.4k
21 votes
4 answers
1k views

What's wrong with this FFT-based Von Kármán vortex street simulation?

About 9 years ago, I came across this interesting website, and found the following paragraph with a broken Mathematica code sample: When fluid passes an object, it can leave a trail of vortices ...
xzczd's user avatar
  • 65.4k
6 votes
4 answers
3k views

Why does Fourier give a shifted frequency?

I have a signal that I want to identify the frequencies in it, I used the Fourier function but I can't get the frequency correctly. Here is a simplified example: ...
xslittlegrass's user avatar
14 votes
2 answers
3k views

How can I use fast Fourier transform (FFT) to solve a PDE (heat equation)?

I'm trying to solve a one-dimensional heat equation (PDE) with the Fourier transform numerically, in the way it was done here. The equation: , is subject to the initial condition: , where U(x,t) is ...
SAC's user avatar
  • 1,335
11 votes
2 answers
2k views

Correct Fourier scaling and high-resolution frequency identification

I have a dataset of amplitude versus time $(t,A(t))$ and I need to extract the dominant frequency and amplitude, and also get the amplitude at one other specific frequency. My data looks like this: <...
rhermans's user avatar
  • 36.3k
7 votes
2 answers
3k views

Frequencies represented in a DFT list (Fourier[])

I have a sound sample (sample rate: 44100). When I have a list l with n successive elements from the sample, ...
Coolwater's user avatar
  • 20.2k
5 votes
1 answer
3k views

Differences between FFT and analytical Fourier Transform

In MATLAB, if I perform an FFT on a simple Gaussian spot with a phase grating: ...
user12800's user avatar
6 votes
2 answers
646 views

Convert MATLAB code solving 1D wave equation via FFT using ode45 into Mathematica code

I don't quite understand the process of solving differential equations by MATLAB. It seems that it doesn't need the explicit function to specify the required solution, but only needs to input the ...
mozeq's user avatar
  • 295
5 votes
1 answer
5k views

Discrete Fourier Transform with x axis data?

Usually, Fourier Transform in mathematica is supplied by y data only, like the famous Sin[x] transform example. What if my data is a list of ...
bboczeng's user avatar
  • 449
5 votes
1 answer
367 views

Why does Fourier give me a different picture than ImagePeriodogram?

I want to take a 2D fourier transform of some data, but when I try this I get unexpected results. When I use ImagePeriodogram I get something that looks like I ...
AccidentalTaylorExpansion's user avatar

15 30 50 per page