MATLAB event function help

Hi, new to matlab and doing the academy courses to help, running through the ODE course and coming to an example where they suggest adding an event function to stop the calculation when a projectile hits the ground.

Its a series of 2 odes and its a simple code:

tRange = [0 3];
Y0 = [0 20];

[tSol,YSol] = ode45(@myode,tRange,Y0)

h = YSol(:,1)
plot(tSol,h)

function dYdt = myode(t,Y)

h = Y(1);
u=Y(2);

dhdt = u;
dudt = -9.8;

dYdt = [dhdt;dudt];
end

from the event function page I think you are supposed to set it up as:

options = odeset('Events',@event_function)
[tSol,YSol,te,ye,ie] =(@myode,tRange,Y0,options)

function [value,isterminal,direction] = event_function(t,h)

value = (Y(1) ~= 0); 
isterminal = 1; 
direction = 0;

but get a load of errors, what am I doing wrong?

Answer 1

[Torsten]

function main
tRange = [0 10];
Y0 = [0 20];
options = odeset('Events',@event_function)
[tSol,YSol,te,ye,ie] =ode45(@myode,tRange,Y0,options)
h = YSol(:,1);
plot(tSol,h)
end

function [value,isterminal,direction] = event_function(t,h)

value = h(1); 
isterminal = 1; 
direction = 0;
end

function dYdt = myode(t,Y)

h = Y(1);
u=Y(2);

dhdt = u;
dudt = -9.8;

dYdt = [dhdt;dudt];
end

Answer 2

[Walter Roberson]

tRange = [0 3];
Y0 = [0 20];

options = odeset('Events',@event_function);
[tSol,YSol,te,ye,ie] = ode45(@myode,tRange,Y0,options);

h = YSol(:,1);
plot(tSol,h)

function dYdt = myode(t,Y)

h = Y(1);
u=Y(2);

dhdt = u;
dudt = -9.8;

dYdt = [dhdt;dudt];
end

function [value,isterminal,direction] = event_function(t,Y)

value = (Y(1) ~= 0); 
isterminal = 1; 
direction = 0;
end

[Peter Delaney]

Hi, Thanks for your help, when I run the code I still get this error messaged:

Undefined function 'sign' for input arguments of type 'logical'.

Error in odezero (line 46) indzc = find((sign(vL) ~= sign(vR)) & (direction .* (vR - vL) >= 0));

Error in ode45 (line 353) odezero(@ntrp45,eventFcn,eventArgs,valt,t,y,tnew,ynew,t0,h,f,idxNonNegative);

Error in reaction (line 4) [tSol,YSol,te,ye,ie] = ode45(@myode,tRange,Y0,options);

Answer 3

[Peter Delaney]

Perfect, thank you!!