Section: Transforms/Decompositions
y = fftn(x)
which computes the same-size FFTs for each dimension of x.
Alternately, you can specify the size vector
y = fftn(x,dims)
where dims is a vector of sizes. The array x is zero padded
or truncated as necessary in each dimension so that the output
is of size dims. The fftn function is implemented by a sequence
of calls to fft.