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Conditionally execute a function inside a vector field while integrating with an ODE solver

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Ícar
Ícar on 4 Jun 2021
Commented: darova on 7 Jun 2021
I am integrating some equations that represent an astrodynamics problem. They are defined by a vector field such as:
where x are the states (e.g. position, velocity, mass...). The dynamics that I'm integrating are fed by a control u, that is computed based on the states and time: . This control u is computed inside the vector field, which we could explicitely state as . I am integrating with an ODE solver (e.g. ode45()), and thus the solver computes the control at every time step.
Now, what I want is to avoid computing the control at every time step, but rather only at certain times, with a given frequency (e.g. let's say I want to compute the control at 0.1 Hz, every 10s). How would you recommend me to approach this?
I hope I was clear enough. Thank you for any help.

Answers (1)

darova
darova on 5 Jun 2021
Try to pass your condition inside ode function
An example
function dy = func1(t,x)
tset = [10 20 30];
if any(abs(t-tset)>0.05)
u = x(1)*t-1;
end
% dy function ...
end
function main
[t,y] = ode45(func1,tspan,x0);
plot(t,y)
end
  2 Comments
darova
darova on 7 Jun 2021
  • will execute the control if we are close to a pre-scribed epoch with a resolution of 0.05s.
You are right, my bad

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