This is the basic structure for solving the ode.
u0 = 2;
v0 = 0;
tspan = [0 5];
k = 1;
a = 25;
[t,U] = ode45(@odefn, tspan, [u0 v0],[],k,a);
u = U(:,1);
v = U(:,2);
plot(t,u),grid
xlabel('t'),ylabel('u')
function dUdt = odefn(~,U,k,a)
u = U(1);
v = U(2); % v = du/dt
dvdt = k*(1-u^2)*v - a*u;
dUdt = [v;
dvdt];
end
You could investigate fzero to get the value of k that gives 1.25 beats/sec, or adjust it manually (as I did here to get an approximate value).
