ODE event location but integration does not stop

I am trying to use the “Events” option of the odeset function to stop the solver integration of the ODE system at “steady state” (where vector dydt = 0), but the solver never stops (only when it reaches Inf [t = ~10^300]).

%% event function (saved as function file)

function [x,isterm,dir] = eventfun(t, y, parameters, rates)

dydt = cellmodel_odes(t, y, rates, parameters)

dy = norm(dydt, Inf)

x = dy

isterm = 1;

dir = 0;

end

%% script calling event function

% call solver routine

...

t0= 0;

xoverFcn = @(T, Y) eventfun(T, Y, parameters, rates);

opts = odeset('Events',xoverFcn);

[t,y]= ode15s(@(t,y) cellmodel_odes(t, y, rates, parameters), [t0 Inf], init, opts);

...

[Chinmay]

did you find a solution?

[Torsten]

An exact steady state (thus norm(dydt) = 0 exactly) is impossible to reach.

Say you have the differential equation

dy/dt = -y, y(0) = 1

with solution

y(t) = exp(-t).

Steady state is y = 0, but it is never reached.

Thus you will have to set a small value at which the solver should stop, e.g.

%% event function (saved as function file)
function [x,isterm,dir] = eventfun(t, y, parameters, rates)
  dydt = cellmodel_odes(t, y, rates, parameters)
  small = 1e-8;
  dy = norm(dydt, Inf) 
  x = dy - small;
  isterm = 1;
  dir = 0;
end