The event that I set in ode15s doesn't happen. ADE problem.

Hi,

I set an event in my ADE problem using ode15s to stop the integration when the event happens. The problem is that the independent variable only has a small step at the beginning, so when my variables are near the event they get suddenly a higher value so the event is not detected.

I´m integrating Xdot=x(1), Ydot=x(2), Zdot=x(3), where Xdot,Ydot,Zdot represents velocitys. I want my Algorithm to stop at a distance DIST from P, that represents a certain point. I´m sure my trajectory pass through P.

My event is the next one:

function [valor,fin,direccion]=efunxdotWP(t,x,P,DIST) valor=norm([P(1)-x(1),P(2)-x(2),P(3)-x(3)])-DIST; fin=1; direccion=0;

I observed that "valor" decreases but, when it is near 0, suddenly grows. Thus, the point get away from P because the event is not detected.

Do you know how to fix it?

Thank you very much.

Edit: I have tried to fix it using a DIST higher. In this way, I get negative values of "valor" when the event is near and I achieve convergence. Do you think there is another way?

Edit2: I found out what was happening.The behavior of my function is linear so, in order to save time, the ode15s got a big step since certain time. I used 'MaxStep' inside of odeset options in order to control the biggest feasible step. Thanks to 'MaxStep' I can stop the integration when the event has to happen.

I hope "Edit2" will be useful. Bye!