error in line 15 at initial conditions please help

function dydt = pendulum_system(t, y)
g = 9.81;  % Acceleration due to gravity
L = 1.0;   % Length of the pendulum

theta = y(1);
omega = y(2);

dtheta_dt = omega;
domega_dt = -omega - (g/L) * sin(theta) + cos(0.2*t);

dydt = [dtheta_dt; domega_dt];
end
% Initial conditions
initial_conditions = [pi/4; 0];
% Solve the ODE system
[t, Y] = ode45(@pendulum_system, [0 200], initial_conditions);
% Plotting
figure;
plot(t, Y(:, 1));
xlabel('Time (s)');
ylabel('Theta (radians)');
title('Solution of Pendulum ODE for Theta');
grid on;

Answer 1

[Sulaymon Eshkabilov]

This is how the code should be put together and executed:

% Initial conditions
initial_conditions = [pi/4; 0];
% Solve the ODE system
[t, Y] = ode45(@pendulum_system, [0 200], initial_conditions);
% Plotting
figure;
plot(t, Y(:, 1));
xlabel('Time (s)');
ylabel('Theta (radians)');
title('Solution of Pendulum ODE for Theta');
grid on;

%% pendulum_system is a nested function:
function dydt = pendulum_system(t, y)
    g = 9.81;  % Acceleration due to gravity
    L = 1.0;   % Length of the pendulum
    
    theta = y(1);
    omega = y(2);
    
    dtheta_dt = omega;
    domega_dt = -omega - (g/L) * sin(theta) + cos(0.2*t);
    
    dydt = [dtheta_dt; domega_dt];
end