I want to do a stop condition in ode45 that he demands dx=0

this is my code And I don't understand why it doesn't work :(

AnonFun=@(t,x)(5*x-1*x^2);
Opt=odeset("Events",@myEvent);
[t,x]=ode45(AnonFun,[0,5],1,Opt);
plot(t,x)
function [value, isterminal, direction] = myEvent(t,x)
value = diff(x)==0;
isterminal = 1;   % Stop the integration
direction  = -1;
end

Im trying to get this :

Answer 1

[Torsten]

AnonFun=@(t,x)(5*x-1*x^2);
Opt=odeset("Events",@(t,x)myEvent(t,x,AnonFun));
[t,x]=ode45(AnonFun,[0,5],1,Opt);
plot(t,x)

function [value, isterminal, direction] = myEvent(t,x,AnonFun)
value = AnonFun(t,x)-1.0e-4;
isterminal = 1;   % Stop the integration
direction  = -1;
end

[shir hartman]

Hey thanks ,

My intention is to stop the calculation operation.

[Torsten]

There is no sign-change in dx/dt from positive to negative. So I changed the code above to stop when

dx/dt < 1e-4.

[shir hartman]

thanks!!!

Answer 2

[Walter Roberson]

You need to carry around one more level of derivatives.

AnonFun = @(t, x) [x(2); 5-2*x(1)];

Opt = odeset("Events", @myEvent);
[t, x] = ode45(AnonFun, [0,5], [1, 5], Opt);
plot(t, x(:,1))

function [value, isterminal, direction] = myEvent(t, x)
    value = x(2);
    isterminal = 1;   % Stop the integration
    direction  = -1;
end

[shir hartman]

Hi, first of all thanks.

But what I wanted to get was the orange graph (which is the function) - simply that it will stop calculating from the moment the derivative resets (when the function is constant)