function mydft(x)
    N=length(x)
    y=Array{Complex}(undef,N)
    for l=0:N-1
        a=exp.(-1im*2*pi*l/N*(0:N-1))
        y[l+1]=a'*x
    end
    return y
end

for n=2:14
    N=2^n
    x=rand(N)
    println("N=",N)
    @time xhat=mydft(x)
#   println("x=",x)
#   println("xhat=",xhat)
end