MATLAB: Help on plot 3 roots for each variable and connecting them

for looppidpid controllerplotplottingroots

I'm trying to plot the roots coming out of the this code but after I Run the code, no graph shows up. I know that for each variable K_p_no, there's 3 roots because the pol variable shows up in the Workspace with 3 roots in a single cell. How can I find the roots of the equation and plot them all in the same graph? If possible, also connect them. This is for a PID controller but without the ID, if it helps in any way.
clc; clear all; close all;
n = 10;
K_p_neg_inf = -1000;
K_p_pos_inf = 1000;
K_p_no = K_p_neg_inf:n:K_p_pos_inf;
for i=1:length(K_p_no);
    ChEq{i} = [K_p_no(i)*50 K_p_no(i)*100 1 K_p_no(i)*60]; %characteris eqn (K_p*50*s^2 + K_p*100*s + s^2 + K_p*60) of the T_s, set =0 to find the poles in the s-plane
    pol{i} = roots(ChEq{i}); %poles on s-plane
    
    plot(real(poles), imag(poles), 'rx')
    xlabel('Real Axis (seconds^-1)');
    ylabel('Imaginary Axis (seconds^-1)')
    grid on
end

Best Answer

See if this slightly edited version of your code does what you want: 
n = 10;
K_p_neg_inf = -1000;
K_p_pos_inf = 1000;
K_p_no = K_p_neg_inf:n:K_p_pos_inf;
figure
hold on
for i=1:length(K_p_no);
    ChEq{i} = [K_p_no(i)*50 K_p_no(i)*100 1 K_p_no(i)*60]; %characteris eqn (K_p*50*s^2 + K_p*100*s + s^2 + K_p*60) of the T_s, set =0 to find the poles in the s-plane
    pol{i} = roots(ChEq{i}); %poles on s-plane
    
    plot(real(pol{i}), imag(pol{i}), 'rx')
    xlabel('Real Axis (seconds^-1)');
    ylabel('Imaginary Axis (seconds^-1)')
end
hold off
grid
.
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