euler.v

import math

fn forward_euler(timestep f64, n int) []f64 {
	mut res := [f64(0.0)].repeat(n)
	res[0] = f64(1)
	for x := 1; x < n; x++ {
		res[x] = res[x-1] - 3.0*res[x-1]*timestep
	}
	return res
}

fn check(result []f64, threshold, timestep f64) bool {
	mut approx := true
	for x := 0; x < result.len; x++ {
		solution := math.exp(-3.0 * f64(x) * timestep)
		if math.abs(result[x]-solution) > threshold {
			tmp := result[x]
			println("There is a mismatch: abs($tmp-$solution) > $threshold!")
			approx = false
		}
	}
	return approx
}

fn main() {
	timestep := .01
	threshold := .01
	n := 100

	result := forward_euler(timestep, n)

	if check(result, threshold, timestep) {
		println("All values within threshold")
	} else {
		println("Value(s) not within threshold")
	}
}