Put a condition on 't' in ode15s ? Imp. question

function F = zero_order(t,~)
global k st_t
a = 1/k ;   % here k is an input

if t <= a ;
    k = k;
else 
    k = 0;
end
F(1) = -k;
F(2) = k;

st_t =[st_t ; t  a k];
F=F';
end

inital cond = [1 0];

The problem in the above code is that , as ode15s is adaptive time step, it gives output according to the time span I give to the equation i.e. according to the time step value just before the point when conditions change.

So say the time when k in the above code should be zero is at t=50 seconds. at that point, x(1) = 0 and x(2) = 1; but depending on the time step before the same. it calcultes and gives the output

x(1) = 0.8 and x(2) = 0.2;

and this values changes according to the time span I enter, at large t_span it gives me the correct values , while at lower time span size it gives me other values (not expected)

The crux of the question is : Is there a way by which I can insure that it calculates values at the given time i.e. t= 1/k in the above case.

Sorry if the question is not clear, Shall elaborate if required , Thanks, Tonu

[Edited, Jan, code formatted]

Answer 1

[Titus Edelhofer]

Hi,

yes, that's possible. It's the "event location property". Take a look at

doc odeset

and look there for "Events". Add 1/k as an event ...

Titus

[Tonu]

Hey thanks Titus for your reply, Can you further suggest me how to insert the 'events' in my code, my attempt fails.

THanks, Tonu