fmi-sim 0.5.0

A pure Rust FMI simulator
Documentation 
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use super::{Model, Solver, SolverError};

pub struct Euler {
    /// Current time
    time: f64,
    /// Continuous states
    x: Vec<f64>,
    /// Derivatives of continuous states
    dx: Vec<f64>,
    /// Event indicators
    z: Vec<f64>,
    /// Previous event indicators
    prez: Vec<f64>,
}

impl<M: Model> Solver<M> for Euler {
    type Params = ();

    fn new(start_time: f64, _tol: f64, nx: usize, nz: usize, _solver_params: Self::Params) -> Self {
        Self {
            time: start_time,
            x: vec![0.0; nx],
            dx: vec![0.0; nx],
            z: vec![0.0; nz],
            prez: vec![0.0; nz],
        }
    }

    fn step(&mut self, model: &mut M, next_time: f64) -> Result<(f64, bool), SolverError> {
        let dt = next_time - self.time;

        if !self.x.is_empty() {
            model.get_continuous_states(&mut self.x);
            model.get_continuous_state_derivatives(&mut self.dx);

            for i in 0..self.x.len() {
                self.x[i] += self.dx[i] * dt;
            }

            model.set_continuous_states(&self.x);
        }

        let mut state_event = false;

        if !self.z.is_empty() {
            model.get_event_indicators(&mut self.z);

            self.z
                .iter()
                .zip(self.prez.iter_mut())
                .for_each(|(z, prez)| {
                    // crossed zero going positive
                    let cross_pos = *prez <= 0.0 && *z > 0.0;
                    // crossed zero going negative
                    let cross_neg = *prez > 0.0 && *z <= 0.0;
                    state_event = cross_pos || cross_neg || state_event;
                    *prez = *z;
                });
        }
        self.time = next_time;

        Ok((self.time, state_event))
    }

    fn reset(&mut self, model: &mut M, _time: f64) -> Result<(), SolverError> {
        if !self.z.is_empty() {
            model.get_event_indicators(&mut self.z);
        }
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    struct SimpleModel;

    impl Model for SimpleModel {
        fn get_continuous_states(&mut self, x: &mut [f64]) {
            x[0] = 0.0;
        }

        fn set_continuous_states(&mut self, states: &[f64]) {
            assert_eq!(states[0], 1.0);
        }

        fn get_continuous_state_derivatives(&mut self, dx: &mut [f64]) {
            dx[0] = 1.0;
        }

        fn get_event_indicators(&mut self, z: &mut [f64]) {
            z[0] = 0.0;
        }
    }

    #[test]
    fn test_euler() {
        let mut euler = <Euler as Solver<SimpleModel>>::new(0.0, 1e-6, 1, 1, ());
        let (time, state_event) = euler.step(&mut SimpleModel, 1.0).unwrap();
        assert_eq!(time, 1.0);
        assert!(!state_event);
    }
}