It is just a Fact Of Life with MATLAB. You have some non-function statements, then you define a function, then you end the function, then you have more non-function statements. MATLAB considers your script (the original non-function statements) to have ended as soon as the first function definition appeared, and doesn't know what to do with the non-function statements after the function definition. Just move the function definition to the end.
global alpha
global beta
% Y = [x(t) y(t)], Y(1) = x(t), Y(2) = y(t)
alpha = 0.1;
beta = 0.1;
for x0 = [0:0.05:0.5]
alpha = 0.1
beta = 0.1
fig = figure;
[t_array, Y_array] = ode45(odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
alpha = 0.05;
beta = 0.2;
for x0 = [0:0.05:0.5]
fig = figure;
[t_array, Y_array] = ode45(@odefun, [0:200], [x0 0]);
plot(t_array, Y_array)
end
function [dx_dt dy_dt] = odefun(t, Y)
x = Y(1); y = Y(2);
global alpha
global beta
dx_dt = beta * (1 - x - y) * x - alpha * x;
dy_dt = alpha * x;
end
