how to stop dde23 when one of states reach certain value?

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sourabh mittal 2018-9-18

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评论： sourabh mittal 2018-9-18

I want to stop dde23 when i am geeting 99% close to steady state and extract saturation time. I have written code of my system and then call dde23 to solve it. problem is am not able to terminate code when saturation is reached.

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Answer 1

Torsten 2018-9-18

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Use the "Events" option of dde23.

Best wishes

Torsten.

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Torsten 2018-9-18

在 MATLAB Online 中打开

function main
  tstart = 0.0;
  tend = 100.0;
  options = ddeset('Events',@events);
  sol = dde23(@ddex1,2,[0.7],[tstart tend],options);
  tevent = sol.xe(1)   % time of 99 % saturation
  tint = linspace(tstart,tevent,20);
  yint = deval(sol,tint);
  plot(tint,yint)
end
function dydt = ddex1(t,y,Z)
  ylag = Z(:,1);
  dydt = y*ylag*(1-y);
end
function [value,isterminal,direction] = events(t,y,Z)
  value(1) = y(1)-0.99;
  isterminal(1) = 1;
  direction(1) = 1;
end

sourabh mittal 2018-9-18

Thank you!

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Answer 2

Walter Roberson 2018-9-18

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https://www.mathworks.com/help/matlab/ref/ddeset.html

Perhaps relax RelTol ?

The normal way of stopping early is to use an event function that examines the current state and decides whether to terminate early.

However, I do not know how you would determine whether saturation has occurred. If it requires examining previous states, such as to determine that the change in values is small enough, then event functions cannot do that (but in that particular situation, changing tolerances can help.)