How to store values in a matrix to plot later?

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James Metz
James Metz on 25 Nov 2020
Edited: James Metz on 26 Nov 2020
I am trying to create a pandemic simulation to account for several variables, store these values in a single matrix, and then plot these values on a graph. I'm having some trouble with this. My graphs are not showing up as expected and I'm not sure what the problem is. Please help. Thanks.
Here's my code:
%Epidemic Simulation
%Author: James Metz
%Date: Nov 15, 2020
%Define Natural Paramteres:
p = 0.0144; %Natural Birth Rate (Davidson County)
u = 0.008; %Natural Death Rate (Davidson County)
f = 0.03; %Infection Rate
r = 0.075; %Recovery Rate
m = 0.0001; %Death due to Infection Rate
v = 0.092; %Vaccination Rate
%Define Evaluation Time Paramteres:
dt = 1; %Time increments (days)
tEnd = 365; %Simulation length (days)
t = 1:dt:tEnd;
%Initialize Variables:
I = 10; %Initial infected population
R = 0; %Initial recovered population
S = 692587; %Initial susceptible population
I_1d = zeros(1, tEnd);
R_1d = zeros(1, tEnd);
S_1d = zeros(1, tEnd);
S_1d(1) = 692587;
I_1d(1) = 10;
R_1d(1) = 0;
%Loop through times:
for idx = 2:dt:tEnd
S = S_1d(idx - 1);
R = R_1d(idx - 1);
I = I_1d(idx - 1);
%Find changes in population numbers
dS_dt = -f*S*I - S*u - S*v + S*p; %Drop in unifected population
dI_dt = f*S*I - r*I - m*I - u*I; %Drop in infected population
dR_dt = r*I + S*v - u*R; %Gain in Recovered population
%Store new values:
S_1d(idx) = S_1d(idx-1) + dS_dt;
R_1d(idx) = R_1d(idx-1) + dR_dt;
I_1d(idx) = I_1d(idx-1) + dI_dt;
plot(t, S_1d)
xlabel('Time (days)')
ylabel('Susceptible Population')
title('Drop in Susceptible Population due to Infection')
plot(t, R_1d)
xlabel('Time (days)')
ylabel('Recovered Population')
title('Recovery Rate of Infected Persons')
plot(t, I_1d)
xlabel('Time (days)')
ylabel('Infected Population')
title('Infection Rate of Susceptible Persons')
subplot(2, 2, 4)
plot(t, S_1d, 'green')
plot(t, R_1d, 'Blue')
plot(t, I_1d, 'red')
my graphs look like this:

Answers (1)

Sibi on 25 Nov 2020
Try this , you should not multiply the infected population to sucesptible population
dS_dt = -f*S - S*u - S*v + S*p;
dI_dt = f*S - r*I - m*I- u*I;
dR_dt = r*I + S*v- u*R;
  1 Comment
James Metz
James Metz on 26 Nov 2020
Edited: James Metz on 26 Nov 2020
The equations are based on the SIR model.
See link for more information:
But thank you.

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