MATLAB: Hold on not working for plotting transfer function MATLAB

MATLABplottransfer function

%% DATA
k1 = (1.5+0)/2;            % Should be unstable
k2 = 1.5;                  % Should be marginally stable
k3 = (1.5+2.5)/2;          % Should be stable



k4 = 2.5;                  % Should be stable
k5 = (57.5+2.5)/2;         % Should be stable
k6 = 57.5;                 % Should be stable
k7 = 1000;                 % Should be stable 
x = [k1,k2,k3,k4,k5,k6,k7];
% Vector of ks
t = 0:.01:5;
steps = ones(1,length(t));   % Input - step
t_f = tf([1 18] , [1 6 -27]);
color = ['g','b','r','y','m','k','c']; % color of plots
m=1;
hold on
for i = 1:length(x)
    t_f = tf(x(i)*[1 18] , [1 6+x(i) -27+18*x(i)]);
    result(i) = t_f;
    y = lsim(result(i),steps,t); 
    % figure(i)       When I use this method it actually plots the transfer functions
    plot(t,y,color(:,m),'linewidth',1.5) % Plot w/ different colors
    m = m + 1;    % var to change color
end
legend({'k1','k2','k3','k4','k5','k6','k7'},'Location','NorthWest') 
hold off
I don't understand why it doesn't plot the rest of my x matrix. It plots the first value, x(1), then it just gives me lines = 0 of different colors. When I use figure(i), it works, but that's not what I need right now. Any suggestions? thanks

Best Answer

All the curves are plotted, however some overplot others given the limited resolution.
Change the plot call to: 
plot(t(y>1E-4),y(y>1E-4),color(:,m),'linewidth',1.5) % Plot w/ different colors
set(gca, 'YScale','log')
to see them, although some are barely visible. (For some reason that I did not explore, semilogy does not work here.)
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