update

% 3.5最后一问

function a=dtfs(x,n_init);

if n_init==0

    a=1/length(x)*fft(x);

else if n_init<0

a=[];

w=2*pi/length(x);  %fundamental frequency

    for k=n_init:n_init+length(x)-1  %period from 0+n0 to N-1+n0

        a_k=0;

            for n=1:length(x)

             a_k=a_k+x(n)*exp(-j*k*w*(n+n_init-1));

            end

        a=[a a_k/length(x)];

    end

    if n_init<0

        for i=1:-n_init

            x=[x x(i)];

            a=[a a(i)];

        end

        x=x(1-n_init:length(x));

         a=1/length(x)*fft(x);

    else n_init>0

        a=a(1-n_init:length(a));

    else if n_init>0

        for i=i:n_init

            x=[x(length(x)-i+1) x];

            a=[a(length(a)-i+1) a];

        end

        x=x(1:length(x)-n_init);

        a=1/length(x)*fft(x);

        a=a(1:length(x));

    end

end

 No newline at end of file