Identifying wave-number sign after FFT2

4 次查看(过去 30 天)
I am plotting a simple wave equation y=Acos(kx-wt) in time 't' and space 'x' domain (i.e. a color plot in 2D domain). Here A,k and w denote amplitude, wave-number and angular frequency respectively.
I then do FFT2 of function y in 2D domain and use function fftshift in order to get low frequency components at the center. I now take only 'positive' angular frequency values hence just half of the domain.
As a result I have all wave-number values (both positive and negative) with only positive angular frequency. I notice that my solution has 'negative' wave-number, which indicates that wave is propagating towards -X direction. However it is not the case with the analytical expression: y=Acos(kx-wt). It is clearly a wave propagating in +X direction.
I would like to know what is the correct way of interpreting FFT2 results in terms of signs of wavenumber.
A sample code is attached.
Thank you in advance, Rajesh
  1 个评论
Rik 2020-11-2
Regarding your flag as unclear: you received an answer below.
In case you try to remove your question: anyone with editing privileges will be able to restore it from this backup.


回答(1 个)

Youssef  Khmou
Youssef Khmou 2014-12-27
The general solution for a wave travelling in the +X direction is, at point X :
y(0,t)=A exp(j(wt))
y(X,t)=A exp(j(wt-KX));


Help CenterFile Exchange 中查找有关 Spectral Measurements 的更多信息


Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by