Adding a horizontal line to a plot

How do you use the line function to add a horizontal line to a plot?

For example,

To add a horizontal line to easily point out the maximum value.

I am trying to use it in a nested for loop. This is my code so far:

y =[99;1;0];
beta = [0.005, 0.05, 0.1];
nu = [0.05, 0.075, 0.1];
options=odeset();
for i = 1:length(beta) 
    for index = 1:length(nu)
        [T,Y] = ode45(@sir_ode,[0 30], y,options,beta(i),nu(index));
        figure
        plot(T,Y)
        xlabel('Time(days)')
        ylabel('Population(%)')
        legend('susceptible','infected','recovered')
        title_name =sprintf('Beta = %.3f Nu = %.3f', beta(i), nu(index));
        title(title_name)
        % finds max infected values
        infected_values = Y(:,2);
        max_infected(i,index) = max(infected_values);
        % find max time
        index_number(i,index)=find(infected_values ==max(infected_values));
        max_T(i,index) = T(index_number(i,index));
        line([max_T(i),max_T(i)], ...
            [0,max_infected(i)],'Color', [0 1 0])
   end 
end

Thank you.

Answer 1

[Star Strider]

I couldn’t run your code. You can do something like this to plot a horizontal line at the maximum:

x = linspace(0,pi);
y = sin(x);

ymax = max(y);

figure(1)
plot(x, y, '-b')
hold on
plot(xlim, [1 1]*ymax, '-r')
hold off
axis([xlim    0  1.1])

[Simone]

Thank you for your help!

[Star Strider]

My pleasure!

Answer 2

[Image Analyst]

Your line is a vertical line because both the x values are the same. To get a horizontal line, from the x=0 (y) axis to the peak, you could do

[maxY, indexAtMaxY] = max(infected_values);
x1 = 0;
x2 = T(indexAtMaxY);
line([x1, x2], [maxY, maxY], 'Color', 'g', 'LineWidth', 2);

[Image Analyst]

Needless to say, all that code about "index_number" is unnecessary so get rid of it.