# Finite Fourier Transform on a 3d wave

brandy
Finite Fourier Transform on a 2d wave

How does the finite Fourier transform work exactly?

The transform of f(x) is
$\widetilde{f}(\lambda_{n})$ =$\int$$^{L}_{0}$ f(x) X$_{n}$ dx

If I had a 3d wave equation pde and I applied Finite Fourier transform on the pde for
z(x,y,t)=X(x)Y(y)T(t)

f(x)=z$_{xx}$
$\tilde{z_{xx}(\lambda_{n})}$ =$\int$$^{L}_{0}$ z$_{xx}$ X$_{n}$(x) dx

f(x)=z$_{yy}$
$\tilde{z_{yy}(\lambda_{n})}$ =$\int$$^{L}_{0}$ z$_{yy}$ Y$_{n}$(y) dy

etc for T

or

is the transform the same for everything, namely:
f(x)=z$_{xx}$
$\tilde{z_{xx}(\lambda_{n})}$ =$\int$$^{L}_{0}$ z$_{xx}$ X$_{n}$(x) Y$_{n}$(y) dx

or is it a double integral?
or do you apply finite Fourier twice with respect to y and x.

Last edited:

Homework Helper
MHB
Hi brandy!

You can take any transform you want, including a 3D Fourier transform, which would be a triple integral.
And also a transform of for instance ##z_{xx}## with respect to y.

In all cases you can apply the Fourier's theorems.
It's just a matter of what you want to achieve.

Note that you should have a different "frequency" variable for each dimension $x$ and $y$.