What is wrong with my SIR Model?

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Eymen Dogrusever
Eymen Dogrusever 2020-5-26
编辑： praguna manvi 2025-2-3
I tried to use SIR Model for my homework but it doesn't run. This is the question.
• Let S(t) denote the number of susceptible at time t (in hours).
• Let I(t) denote the number of infected individuals at time t (in hours).
• Let R(t) denote the number of recovered individuals at time t (in hours).
Use MATLAB’s or R’s built-in functions (i.e. ode45 or deSolve) to solve the following system of ODEs from t = 0 to t = 720 hours:
A) The spread of the disease is modeled as
dS/dt= -βSI,
dI/dt = βSI-γI,
dR/dt = γI,
with the initial conditions S(0) = 50, I(0) = 1, R(0) = 0 and γ = 0.0083, β = 0.0006.
clc;
clear;
function dPop=Diff_2_1(t, pop, parameter);
beta=0.0006;
gamma=0.0083;
S=pop(1);
I=pop(2);
R=pop(3);
dPop=zeros(3,1);
dPop(1)= -beta*S*I;
dPop(2)= beta*S*I - gamma*I;
dPop(3)= gamma*I;
end
function [t,S,I,R] = Program_2_1(beta,gamma,S0,I0,MaxTime)
S=S0;
I=I0;
R=1-S-I;
[t, pop]=ode45(@(t,y) Diff_2_1(t,y,[beta gamma]),[0 MaxTime],[S I R]);
S=pop(:,1); I=pop(:,2); R=pop(:,3);
[t,S,I,R] = Program_2_1(0.0006,0.0083,50,1,720);
plot(t,S,"-r",t,I,"-g",t,R,"-b")
xlim([0 200])
xlabel("Time","fontweight","bold")
ylabel("Number","fontweight","bold")
h = legend("S","I","R");
legend(h,"show")
end
The code doesn't run. I mean there is no output. Maybe the problem is because I ended the function in the wrong place but I still don't figure out it. Can you show me where is my mistake?

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回答（1 个）

praguna manvi
praguna manvi 2025-2-3
编辑：praguna manvi 2025-2-3
Ran in:
Hi @Eymen Dogrusever,
As I see you have ended the second function wrongly at the function call "Program_2_1(0.0006,0.0083,50,1,720);" and also "legend" is used incorrectly, here is the corrected version of the above snippet :
clc;
clear;
function dPop = Diff_2_1(t, pop, parameter)
beta = parameter(1);
gamma = parameter(2);
S = pop(1);
I = pop(2);
R = pop(3);
dPop = zeros(3,1);
dPop(1) = -beta * S * I;
dPop(2) = beta * S * I - gamma * I;
dPop(3) = gamma * I;
end
function [t, S, I, R] = Program_2_1(beta, gamma, S0, I0, MaxTime)
R0 = 0; % Initial condition for R
[t, pop] = ode45(@(t, y) Diff_2_1(t, y, [beta gamma]), [0 MaxTime], [S0 I0 R0]);
S = pop(:,1);
I = pop(:,2);
R = pop(:,3);
plot(t, S, '-r', t, I, '-g', t, R, '-b')
xlim([0 200])
xlabel('Time', 'fontweight', 'bold')
ylabel('Number', 'fontweight', 'bold')
legend('S', 'I', 'R') % Directly pass the strings for the legend
end
% Call the function
[t, S, I, R] = Program_2_1(0.0006, 0.0083, 50, 1, 720);
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