main.rs

#![feature(non_ascii_idents)]

use std::io::{Write, BufRead, BufReader};
use std::process::exit;
use std::fs::File;

fn main() {
    let args : Vec<_> = std::env::args().collect();

    if args.len() != 2 {
        writeln!(std::io::stderr(), "Usage: {} FILE", args[0]).unwrap();
        exit(1);
    }

    let reader = BufReader::new(File::open(&args[1]).unwrap());

    let log_pops : Vec<f32> =
        reader.lines().map(Result::unwrap)
        .map(|ref line| line.parse::<u32>().unwrap())
        .map(|pop| f32::ln(pop as f32)).collect();

    let n = log_pops.len() as f32;

    let mut x̅ : f32 = 0.0;
    let mut y̅ : f32 = 0.0;
    let mut s̅q̅r̅x̅ : f32 = 0.0;
    let mut s̅q̅r̅y̅ : f32 = 0.0;
    let mut x̅y̅ : f32 = 0.0;
    
    for (&x, y) in log_pops.iter().zip((1..log_pops.len()).map(|i| f32::ln(i as f32))) {
        x̅ += x;
        s̅q̅r̅x̅ += x * x;
        y̅ += y;
        s̅q̅r̅y̅ += y * y;
        x̅y̅ += x * y;
    }

    x̅ /= n;
    y̅ /= n;
    s̅q̅r̅x̅ /= n;
    s̅q̅r̅y̅ /= n;
    x̅y̅ /= n;

    let m = (x̅y̅ - x̅ * y̅) / (s̅q̅r̅x̅ - x̅ * x̅);
    let sqr_r = (x̅y̅ - x̅ * y̅) * (x̅y̅ - x̅ * y̅) / ((s̅q̅r̅x̅ - x̅ * x̅) * (s̅q̅r̅y̅ - y̅ * y̅));

    println!("m: {}", m);
    println!("R²: {}", sqr_r);
}