problem in simulating an epidemic model using ode45

I am trying to solve and simulate an epidemic model using the guidelines provided by an online tutorial: Here is the function i have defined:

function ypsir = ypsir(t,y) a = 0.25; b = 0.000000908; k = 6; q = 22.02; m = 0.012; p = 0.45; l = 0.25; r = 0.14; ypsir(1) = q - m*y(1)-b*y(1)*y(5)+a*y(4); ypsir(2) = ((1-p)*b*y(1)*y(5))-((m+l)*y(2)); ypsir(3) = (b*p*y(5)*y(1))-((m+r)*y(3))+(l*y(2)); ypsir(4) = (r*y(3))-((m+a)*y(4)); ypsir(5) = ((y(5)/(y(5)+1000))*(exp(10*(y(2)+y(3)))))-(b*k*y(1)*y(5)) ypsir = [ypsir(1) ypsir(2) ypsir(3) ypsir(4) ypsir(5)]';

and i use the following m file to call the above function and plot my graphs:

clear; to = 0; tf = 50; yo = [200 20 20 10 1000000]; [t y] = ode45('ypsirtry',[to tf],yo); plot(t,y(:,1),t,y(:,2),t,y(:,3),t,y(:,4)) xlabel('time') ylabel('susceptible, infected, recovered')

but i am only getting straight lines... seems like the ode45 is not working and the graphs are being plotted for the initial values stated.

Can someone pls help

Answer 1

[David Sanchez]

I tested your code and they are not straight lines, zoom in the plot to see it. Also, check the name of your function

function ypsir = ypsirtry(t,y)
....
...

Then

clear; 
to = 0; 
tf = 50; 
yo = [200 20 20 10 1000000]; 
[t y] = ode45(@(t,y) ypsirtry(t,y),[to tf],yo); 
plot(t,y(:,1),t,y(:,2),t,y(:,3),t,y(:,4)) 
xlabel('time') 
ylabel('susceptible, infected, recovered')

Are you sure your system is what it should be?

[Ojaswita]

Thanks alot for the help! I corrected my mistakes... I do think something is not correct with the system that is showing.. Is there any help I can get?