fft documentation

[parisse]

Let p:=35969;isprime(p); a prime number.
ifactor(p-1); a:=22798;powmod(a,(p-1)/2,p); powmod(a,(p-1)/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);