cons-laws 0.1.5

use mathru::{
    algebra::linear::Vector,
    analysis::differential_equation::ordinary::{problem, ImplicitEuler, ImplicitODE},
};
use plotters::prelude::*;

fn main() {
    // Create an ODE instance
    let problem: problem::Euler<f64> = problem::Euler::default();

    let (x_start, x_end) = problem.time_span();

    let solver: ImplicitEuler<f64> = ImplicitEuler::new(0.0001);

    // Solve ODE
    let (x, y): (Vec<f64>, Vec<Vector<f64>>) = solver.solve(&problem).unwrap();

    println!("{}", x.len());

    // Create chart
    let mut graph_x1: Vec<(f64, f64)> = Vec::with_capacity(x.len());
    let mut graph_x2: Vec<(f64, f64)> = Vec::with_capacity(x.len());
    let mut graph_x3: Vec<(f64, f64)> = Vec::with_capacity(x.len());

    for i in 0..y.len() {
        let x_i = x[i];

        graph_x1.push((x_i, *y[i].get(0)));
        graph_x2.push((x_i, *y[i].get(1)));
        graph_x3.push((x_i, *y[i].get(2)));
    }

    let root_area =
        BitMapBackend::new("./figures/ode_implicit_euler.png", (1200, 800)).into_drawing_area();
    root_area.fill(&WHITE).unwrap();

    let mut ctx = ChartBuilder::on(&root_area)
        .margin(20)
        .set_label_area_size(LabelAreaPosition::Left, 40)
        .set_label_area_size(LabelAreaPosition::Bottom, 40)
        .caption("ODE solved with implicit Euler", ("Arial", 40))
        .build_cartesian_2d(x_start..x_end, -1.0f64..1.5f64)
        .unwrap();

    ctx.configure_mesh()
        .x_desc("Time t")
        .axis_desc_style(("sans-serif", 25).into_font())
        .draw()
        .unwrap();

    ctx.draw_series(LineSeries::new(graph_x1, &BLACK)).unwrap();

    ctx.draw_series(LineSeries::new(graph_x2, &RED)).unwrap();

    ctx.draw_series(LineSeries::new(graph_x3, &BLUE)).unwrap();
}