You define
F=@(t,q) [q(2);(-GM*(q(1)/(((q(1)^2)+q(3)^2)^1.5)))+(g*Functions(t_iter))*(q(2)/(((q(2)^2)+(q(4)^2))^0.5));q(4);(-GM*(q(3)/(((q(1)^2)+q(3)^2)^1.5)))+(g*Functions(t_iter))*(q(4)/(((q(2)^2)+(q(4)^2))^0.5))];
at a time when you have not yet defined t_iter . To use the current value of t_iter you need to move the definition of F to inside your for loop.
Your graphics are wrong. You have
plot(t,q(1,:),'g')
hold on
plot(t,q(1,:),'g')
but q is a 2D array with the same number of rows that t has, with one column per output variable. Perhaps you want plot(t, q(:,1), 'g') . But why do you plot the same thing again?
You also have this plot inside a for loop, causing it to plot each time. But your output is nearly the same each time, so you cannot tell the difference between the lines.
You are looping over t_span but each time calling ode45 for the entire t_span . Why are you doing that? Are you working on a system that has two time dimensions, both of which just happen to be the same size?
