fft documentation

08242017, 05:46 AM
Post: #1




fft documentation
The fft is described as fft(v) and fft(v,a,p), but the version with more than one argument doesn't have the other arguments explained. Can someone please supply that description?
Thx 

08242017, 06:42 AM
Post: #2




RE: fft documentation
(08242017 05:46 AM)webmasterpdx Wrote: The fft is described as fft(v) and fft(v,a,p), but the version with more than one argument doesn't have the other arguments explained. Can someone please supply that description? The current User Guide say this: "With two additional integer arguments a and p, returns the discrete Fourier transform in the field Z/pZ, with a as primitive nth root of 1 (n=size(Vector))." The builtin Help system says almost the same thing but it is missing the word "as", which makes the above confusing. Hope this helps! <0ΙΈ0> Joe 

08242017, 06:45 AM
Post: #3




RE: fft documentation
I don't understand what is meant by a being the nth root of 1.....can you expound?


08242017, 06:48 AM
Post: #4




RE: fft documentation
....or better yet, give an example of doing an fft using these other arguments.


08242017, 07:02 AM
Post: #5




RE: fft documentation
Let p:=35969;isprime(p); a prime number.
ifactor(p1); a:=22798;powmod(a,(p1)/2,p); powmod(a,(p1)/281,p); a is therefore a primitive root of 1 mod p. Take a random vector (modulo p) v:=randvector(128,100); w:=fft(v,a,p); ifft(w,a,p); 

08242017, 11:34 PM
(This post was last modified: 08242017 11:35 PM by webmasterpdx.)
Post: #6




RE: fft documentation
Thank you....that makes a lot more sense. BTW, it might be an idea to add documentation for the randvector function somewhere.... It's in xcas documentation, but nowhere in the prime documentation.
Thx D 

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