Plotting solution curves separately

I am tring to plot the solutions of the SIR model using Runge-kutta fourth order. The graphs are ok but I want to sketch them separatly. I am asking your help how to sketch separatly!! The code is attached

Thank you

Answer 1

[Dyuman Joshi]

% Parameters
c    = 0.0020;
a = 0.02; 
% SIR model (Ordinary Differential Equations)
odefcn = @(t,x) [- c*x(1)*x(2);
                 c*x(1)*x(2) - a*x(2);
                 a*x(2)];
%%The t in the defintion of odefcn feels redundant

% Simulation time span
t0 = 0;
h      = 0.1;   % step size
tf   = 100;
t      = t0:h:tf;	        
% Initial values
y0     = [100 1 1];
% Calling RK4 Solver is similar to ode45 solver
yy = rk4(odefcn, t, y0);

%Define array for legend
str = {'S(t)','I(t)','R(t)'};
%loop to plot in separate figures
for k=1:size(yy,1)
    figure(k)
    % Plotting the solutions
    plot(t, yy(k,:), 'linewidth', 1.5)
    %Change other properties accordingly
    grid on
    xlabel('Time in Days')
    ylabel('Population')
    title('Time responses of SIR model')
    legend(str{k}, 'location', 'best')
end

% Code for Runge-Kutta 4th-order Solver
function y = rk4(f, x, y0)
    y(:, 1) = y0;               % initial condition
    h       = x(2) - x(1);      % step size
    n       = length(x);        % number of steps
        for j  = 1 : n-1
            k1 = f(x(j), y(:, j)) ;
            k2 = f(x(j) + h/2, y(:, j) + h/2*k1) ;
            k3 = f(x(j) + h/2, y(:, j) + h/2*k2) ;
            k4 = f(x(j) + h, y(:, j) + h*k3) ;
            y(:, j+1) = y(:, j) + h/6*(k1 + 2*k2 + 2*k3 + k4) ;
        end
end