ODE45 Event option question

I am trying to use the event option of ODE45 to stop integration when the velocity reaches a certain point (integrating the distance an aircaft travels down a runway). I keep getting the error "SWITCH expression must be a scalar or a character vector." Note: the project requires a Y vector with the top row being the distance down the runway and the bottom row is the velocity)

Here is my event function:

function [value,isterminal,direction] = Events(T,Y2)
% Locate the time when the velocity is over the take off velocity

global Vstall

r=double(Y2 > [0;1.2*Vstall]);

value = r;     % detect 
isterminal = 1;   % stop the integration
direction = 0;   %  negative direction

Thanks!

(wouldn't let me attach thrust:

function [T]=thrust(V)

global nu
global power
global V0

T=nu*(2*power*550)/(V+V0);   % twin engine => 2 * power (power in ft-lb)

end

Answer 1

[Torsten]

My guess is that your r must be

r = Y2(2)-1.2*Vstall

Best wishes

Torsten.

Answer 2

[Raymond Tallarini]

Well I figured it out:

In my ode45 call, I had

[T,Y2]=ode45('ode_DYDT',tspan,x0,options);

I changed it to

[T,Y2]=ode45(@ode_DYDT,tspan,x0,options);

Now it works. Why, i'm not quite sure, but I was tracing how the ballode example works and saw something about Fcnhandleused.

So I don't know why it works now, but it does.

Thanks!