ODE event: Is there a counter ?

Hi, Is there a way to terminate after an event occurs a certain number of times? I am thinking of using a counter in the ODE event function. But I am not sure how to pass it as an argument to the event function.

Thank you,

Sid

Answer 1

[Siddhartha Harsha Ommi]

https://www.mathworks.com/matlabcentral/answers/777882-ode-event-is-there-a-counter#comment_1423231

I am marking my naive approach commented above as the answer for now.

Answer 2

[Kiran Felix Robert]

Hi Siddhartha,

You don’t have to pass the counter as an argument to the event function, you can define the count variable as a global variable (persistent) and increment/decrement it, while not terminating the integration, until the control arrives at a count to terminate the integration.

Refer the answer here (syntax example) and ODE Event Location documentation.

The following snippet can be used as an example, for 10 events.

function [value,isterminal,direction] = Eventsfcn(t,y)
persistent count;
if isempty(count)
    count = 10;
end
if count > 1
    % Your code here
    count = count - 1;
    isterminal = 0;   % Do not stop the integration
else
    % Your Code here
    isterminal = 1; % Stop the integration
end

[Siddhartha Harsha Ommi]

Hi Kiran, But this seems to only keep track of the number of times the Eventsfcn() is called. Am I wrong ?

My question was different. Probably same as the question in the link you have provided. So to make it more clear, if the Eventsfcn() has possibility to track multiple events (say 1] the solution itself reaching a value, 2] the slope and 3] the curvature of the solution vanishing approaching from either positive or negative values), how do I track the number of times one of those events (or each of the events) has occured and eventually stop the integration after a particular limit-count. Below I have written the base code without this feature. Any help is appreaciated.

function [value,isterminal,direction] = Eventsfcn(t,y)
value = [(y(1)-0.5); y(2); y(3)]; % for solution=0.5; slope = 0.0; curvature = 0.0;
isterminal = [0; 0; 0]; % do not terminate in any such event
direction = [0; 0; 0] % such events could occur from either directions

% Now I need a count on let's say how many times the curvature, y(3), has
% vanished approaching from either side. And then stop integration when
% this happens 10 times.
end

Thank you,

Sid

[Siddhartha Harsha Ommi]

To update, I have tried the following naive approach which seemed to work for simpler cases that involve less significant digits. Also, I am not sure how to adapt this to also look at the particular direction from which the event occurs. Probably need to take inspiration from the source code.

function [value,isterminal,direction] = Eventsfcn(t,y)
value = [(y(1)-0.5); y(2); y(3)]; % for solution=0.5; slope = 0.0; curvature = 0.0;
direction = [0; 0; 0] % such events could occur from either directions

persistent cnt;
if isempty(cnt)
    cnt = 0;
end

if y(2)==0 % vanishing curvature. Could be other criteria aswell.
    cnt = cnt + 1;
end

if cnt > 9 % if vanishes 10 times change the terminal
    isterminal = [0; 0; 1];
else
    isterminal = [0; 0; 0]; % default terminal
end

end

However, in my case I am working with a higher number of significant digits and this seemed to be working but only errattically.

Sid