Question - ODE State at time of event #74

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1. martinjrobins commented on Jul 18, 2024

   

   martinjrobins

   on Jul 18, 2024

   Last edited by martinjrobins

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   Hi @JEMH, you can use OdeSolverMethod::interpolate to get the state vector at the time of the event (i.e. t_root).

   If you are happy then continuing the integration from the internal time of the solver, then great :). However, if you wanted to restart from exactly the time of the event, then you would have to mutate the state (using OdeSolverMethod::state_mut) and set it to the interpolated state.

   Perhaps something like this (I havn't tried compiling/running this!)

   let t = loop {
       match solver.step() {
           Ok(OdeSolverStopReason::InternalTimestep) => continue,
           Ok(OdeSolverStopReason::TstopReached) => panic!("We didn't set a stop time"),
           Ok(OdeSolverStopReason::RootFound(t)) => break t,
           Err(e) => panic!("Solver failed to converge: {}", e),
       }
   };
   println!("Root found at t = {}", t);
   let new_state = solver.interpolate(t).unwrap();
   solver.state_mut().unwrap().y.copy_from(&new_state);
   *solver.state_mut().unwrap().t = t;
   solver.step();

   Note that this is inefficient for some solvers (the BDF one) as it needs to be re-initialised after the call to state_mut, so if you are happy to just continue solving without mutating the state (the solver will carry on from its current internal timestep) this is the best.
2. martinjrobins commented on Jul 18, 2024

   

   martinjrobins

   on Jul 18, 2024

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   note I've just put together some docs on this: https://martinjrobins.github.io/diffsol/solving_the_problem.html
3. JEMH commented on Jul 19, 2024

   

   JEMH

   on Jul 19, 2024 via email

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   Thank you for taking the time to answer my question and providing a clear answer. Using your draft code I was able to obtain the state at the event time and then propagate further. The only change that I needed to make to the draft code was to replace the line solver.state_mut().unwrap().copy_from(&new_state); with the two lines solver.state_mut().unwrap().y.copy_from(&new_state); solver.state_mut().unwrap().dy.copy_from(&new_state); The additional documentation „Solving the Problem“ is also very helpful. Regards, James

   …

   Am 18.07.2024 um 20:37 schrieb Martin Robinson ***@***.***>: note I've just put together some docs on this: https://martinjrobins.github.io/diffsol/solving_the_problem.html — Reply to this email directly, view it on GitHub <#74 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABQRDKQSB4BDQVQJU4OXCELZNADNTAVCNFSM6AAAAABLCWFH66VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDEMZXGI2DSOJYGY>. You are receiving this because you were mentioned.
4. Repository owner locked and limited conversation to collaborators on Jul 19, 2024
5. martinjrobins

   converted this issue into a discussion #77 on Jul 19, 2024