Help with ODE45

Hi,

I want to implement a ODE45 solver, but it does not work the way I want, please help!

Situation: I want to model a simple fall of an object that starts falling at a height of 10 meter with no horizontal speed. Only vertical speed and locations are relevant.

Below is my code, and I don't get why it is not working.

options = odeset('AbsTol',1e-6,'MaxStep',5);        % Set some options for ODE45
[t,output] = ode45(@AircraftExit,[0:0.01:10],[10,0],options);  % Set ODE45 odefcn function
global g
g= 9.81
function [bal] = AircraftExit(t,Input)                    % Execute equations of motion
    global g
    bal(1) = Input(2);                              % Velocity                   
    bal(2) = -g;                         % acceleration
end

Answer 1

[Alan Stevens]

global g     % The value of g must be specified before using it in the function via ode45
g = 9.81;
options = odeset('AbsTol',1e-6,'MaxStep',5);        % Set some options for ODE45
[t,output] = ode45(@AircraftExit,0:0.01:10,[10,0],options);  % Set ODE45 odefcn function

function [bal] = AircraftExit(t,Input)                    % Execute equations of motion
    global g
   
    bal = [Input(2);                       % Velocity  
           -g];                            % acceleration
                                              
end