%low pass filter design:
k  = 10000;
zeta = 1.01;
G = tf(k,[1 2*zeta*sqrt(k) k]);

W = logspace(-0.01,3,100)';
[M,P ]= bode(G,W);
M = M(:);
P = P(:);

figure
semilogx(W,M,'b.-');
%draw the cutoffs:
hold on;
plot(W,ones(size(W))*0.988,'b:',W,ones(size(W))*0.2,'b:')