aphreco 0.1.7

A small-scale physiological modeling library
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67

use super::base::StepOptions;

pub struct Rk4<Ode, const LEN_Y: usize>
where
  Ode: Fn(&f64, &[f64; LEN_Y], &mut [f64; LEN_Y]),
{
  ode: Ode,
  h: f64,
  k1: [f64; LEN_Y],
  k2: [f64; LEN_Y],
  k3: [f64; LEN_Y],
  k4: [f64; LEN_Y],
  wk: [f64; LEN_Y],
}

impl<Ode, const LEN_Y: usize> Rk4<Ode, LEN_Y>
where
  Ode: Fn(&f64, &[f64; LEN_Y], &mut [f64; LEN_Y]),
{
  pub fn new(ode: Ode, options: &StepOptions) -> Self {
    let h = match options {
      StepOptions::Default => 1e-3,
      StepOptions::Rk4 { h } => *h,
      _ => panic!("Invalid StepOptions variant."),
    };

    Self {
      ode: ode,
      h: h,
      k1: [0f64; LEN_Y],
      k2: [0f64; LEN_Y],
      k3: [0f64; LEN_Y],
      k4: [0f64; LEN_Y],
      wk: [0f64; LEN_Y],
    }
  }

  pub fn run(&mut self, t: &f64, y: &mut [f64; LEN_Y], dy: &mut [f64; LEN_Y]) -> f64 {
    self.step(t, y, dy);
    t + self.h
  }

  pub fn step(&mut self, t: &f64, y: &mut [f64; LEN_Y], dy: &mut [f64; LEN_Y]) {
    (self.ode)(t, y, &mut self.k1);

    let h_half = self.h / 2.0;
    for i in 0..LEN_Y {
      self.wk[i] = y[i] + self.k1[i] * h_half;
    }
    (self.ode)(&(t + h_half), &self.wk, &mut self.k2);

    for i in 0..LEN_Y {
      self.wk[i] = y[i] + self.k2[i] * h_half;
    }
    (self.ode)(&(t + h_half), &self.wk, &mut self.k3);

    for i in 0..LEN_Y {
      self.wk[i] = y[i] + self.k3[i] * self.h;
    }
    (self.ode)(&(t + self.h), &self.wk, &mut self.k4);

    for i in 0..LEN_Y {
      dy[i] = (self.k1[i] + 2.0 * self.k2[i] + 2.0 * self.k3[i] + self.k4[i]) / 6.0;
      y[i] += dy[i] * self.h;
    }
  }
}