how to stop ode45 when one of states reach certain value

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Mohamed Aburakhis
评论： Walter Roberson 2023-10-20
[x_dot] =derivative(t, x)
x is states [x(1).....x(4)] I need to stop the integration when x(3) reaches 0.1 when the integration stop record (t)

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采纳的回答

Jan
Jan 2016-5-4
Opt = odeset('Events', @myEvent);
[T, Y] = ode45(@YourFun, T, Y0, Opt);
function [value, isterminal, direction] = myEvent(T, Y)
value = (Y(3) == 0.1);
isterminal = 1; % Stop the integration
direction = 0;
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Walter Roberson
Walter Roberson 2023-10-20
@James Gilliam
In the call
[T, Y] = ode45(@YourFun, T, Y0, Opt);
the input T is the timespan to integrate over. It is a vector that must have at least two elements, but may have more. If it has two elements then ode45() will decide by itself what times to output information at; if it has more than two elements then ode45() will output information at the times given in the vector.

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更多回答（2 个）

Walter Roberson
Walter Roberson 2016-5-4
编辑：Walter Roberson 2017-9-13
Gustavo Lunardon
Gustavo Lunardon 2020-8-17
This is confusing. In matlab help it says: An event occurs when value(i) is equal to zero. All answers in this post make it value = 1 for the event to happen. Are the answers outdated somehow?
Source: https://nl.mathworks.com/help/matlab/math/ode-event-location.html
  1 个评论
Walter Roberson
Walter Roberson 2020-8-19
This is a valid concern.
value = (X(8) == 0.05 ) and (Y(3) == 0.1) would happen rarely, when the values were bit-for-bit identical to the representation of 0.05 and 0.1 . One bit different in the representation and the condition will not fire. Better is to write x(8) - 0.05 or 0.05 - x(8), and Y(3)-0.1 or 0.1-Y(3) -- zero crossings can be detected for those.

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