ODE event: Is there a counter ?

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Siddhartha Harsha Ommi
回答： Siddhartha Harsha Ommi 2021-4-15
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

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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.

更多回答（1 个）

Kiran Felix Robert
Kiran Felix Robert 2021-3-22
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
  2 个评论
Siddhartha Harsha Ommi
Siddhartha Harsha Ommi 2021-3-28
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
Siddhartha Harsha Ommi 2021-3-28
编辑：Siddhartha Harsha Ommi 2021-3-28
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

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