odeset: 'Event' as a threshold not zero

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Sylvia Sullivan
Sylvia Sullivan 2016-2-16
评论： Sylvia Sullivan 2016-2-17
I want to halt ode execution and save the output after one of the functions drops below a certain bound. I'm trying to do this with odeset('Events',@events) as follows
function [sol,soln] = fullSScollHM8
% set parameters
options = odeset('Events',@events);
sol2 = ode15s(@fullSSfunc,[t0,tf],init,options);
end
function dy = fullSSfunc(~,y)
dy(1) = ...
dy(7) = ...
end
function [value,isterminal,direction] = events(~,y)
value = y(7) - 10^(-10);
% detect when y(7) gets too low
isterminal = 1; % halt integration
direction = 0; % any which way
end
But if I output value, the code continues to run when y(7) drops below 10^(-10) because value is never zero. It seems like it should be straightforward to define an 'Event' within odeset not with a zero but rather a threshold. Can someone help me please?

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采纳的回答

Walter Roberson
Walter Roberson 2016-2-16
value = y(7) > 10^(-10); %false, 0, when y(7) falls far enough
Remember, a negative value is not a 0 and the termination is to occur when a 0 is detected. The documentation does imply that a crossing should be detected, but does not really state it outright.

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