MATLAB: Conditional with time in ode45

differential equationsfunctionif statementMATLABode45

Hi, how would you change a variable in a function when 't' in ODE45 reaches a certain value? I have already tried formatting it like the code below, but that doesn't work I have also tried using the if statement in the function but then it simply won't read the 't' value. So if I want to change upsilon after a certain time has passed in ODE45 how would I approach this?
clear all, close all, clc
mu = 6.25e10^-3;
eta = 6.25e10^-3;
beta = 0.03813350836;
gamma = 0.01165323939;
delta = 1/7;
alpha = 0.00513392178;
tspan = [1:1:500];
y0 = [0.99 0 0.01 0 0];
[t,y] = ode45(@(t,y)odefcn(y,mu,eta,upsilon,beta,gamma,delta,alpha),tspan,y0);
if t>300
    upsilon = 0.001;
else
    upsilon = 0;
end
plot(t,y)
legend('S','E','I','R','D')
function dydt = odefcn(y,mu,eta,upsilon,beta,gamma,delta,alpha)
dydt = zeros(5,1);
dydt(1) = mu - y(1)*(beta*y(3)+mu+upsilon);
dydt(2) = beta*y(1)*y(3)-y(2)*(mu+delta);
dydt(3) = delta*y(2)-y(3)*(mu+gamma+alpha);
dydt(4) = gamma*y(3)+upsilon*y(1)-eta*y(4);
dydt(5) = alpha*y(3);
end

Best Answer

Include upsilon within the odefcn
mu = 6.25e10^-3;
eta = 6.25e10^-3;
beta = 0.03813350836;
gamma = 0.01165323939;
delta = 1/7;
alpha = 0.00513392178;
tspan = [1:1:500];
y0 = [0.99 0 0.01 0 0];
[t,y] = ode45(@(t,y)odefcn(t, y,mu,eta,beta,gamma,delta,alpha),tspan,y0);
plot(t,y)
legend('S','E','I','R','D')
function dydt = odefcn(t,y,mu,eta,beta,gamma,delta,alpha)
if t>300
    upsilon = 0.001;
else
    upsilon = 0;
end
dydt = zeros(5,1);
dydt(1) = mu - y(1)*(beta*y(3)+mu+upsilon);
dydt(2) = beta*y(1)*y(3)-y(2)*(mu+delta);
dydt(3) = delta*y(2)-y(3)*(mu+gamma+alpha);
dydt(4) = gamma*y(3)+upsilon*y(1)-eta*y(4);
dydt(5) = alpha*y(3);
end
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