How can i construct semilog plot

I want to make a plot error vs N. N sould be in x axis (4,6,8,10,12,14,16). and y exis should be log scale to represent error values. But my code is wrong. How can i do that?

syms j

N=4:2:16;

for i=1:length(N)

    S(i)=(2*pi/(N(i)+1))*(symsum(cos((20*pi*j)/(N(i)+1)),j,0,N(i)));

    A(i)=double(S(i)) ;

end

syms x

f=cos(10*x);

in=double(int(f,[0 2*pi]));

err=A-in;

semilogy(err,N);