#[allow(unused_imports)] use std::cmp::*; // https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8 macro_rules! input { ($($r:tt)*) => { let stdin = std::io::stdin(); let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock())); let mut next = move || -> String{ bytes.by_ref().map(|r|r.unwrap() as char) .skip_while(|c|c.is_whitespace()) .take_while(|c|!c.is_whitespace()) .collect() }; input_inner!{next, $($r)*} }; } macro_rules! input_inner { ($next:expr) => {}; ($next:expr,) => {}; ($next:expr, $var:ident : $t:tt $($r:tt)*) => { let $var = read_value!($next, $t); input_inner!{$next $($r)*} }; } macro_rules! read_value { ($next:expr, ( $($t:tt),* )) => { ($(read_value!($next, $t)),*) }; ($next:expr, [ $t:tt ; $len:expr ]) => { (0..$len).map(|_| read_value!($next, $t)).collect::>() }; ($next:expr, chars) => { read_value!($next, String).chars().collect::>() }; ($next:expr, usize1) => (read_value!($next, usize) - 1); ($next:expr, [ $t:tt ]) => {{ let len = read_value!($next, usize); read_value!($next, [$t; len]) }}; ($next:expr, $t:ty) => ($next().parse::<$t>().expect("Parse error")); } trait Change { fn chmax(&mut self, x: Self); fn chmin(&mut self, x: Self); } impl Change for T { fn chmax(&mut self, x: T) { if *self < x { *self = x; } } fn chmin(&mut self, x: T) { if *self > x { *self = x; } } } fn main() { // In order to avoid potential stack overflow, spawn a new thread. let stack_size = 104_857_600; // 100 MB let thd = std::thread::Builder::new().stack_size(stack_size); thd.spawn(|| solve()).unwrap().join().unwrap(); } fn solve() { input! { n: usize, h: f64, xy: [(f64, f64); n], } let mut a1 = 0.0; let mut a2 = 0.0; // adagrad let mut hsum = 0.0; for _ in 0..1000 { let mut g1 = 0.0; let mut g2 = 0.0; for &(x, y) in &xy { if (x * a2 - y).abs() < (x * a1 + h - y).abs() { g2 += x * (x * a2 - y); } else { g1 += x * (x * a1 + h - y); } } if g1 == 0.0 && g2 == 0.0 { break; } eprintln!("g = {} {}", g1, g2); let g = g1 * g1 + g2 * g2; hsum += g; let coef = 0.4 / hsum.sqrt(); a1 -= g1 * coef; a2 -= g2 * coef; eprintln!("new a = {} {}", a1, a2); } eprintln!("{} {}", a1, a2); let mut ans = 0.0; for &(x, y) in &xy { let tmp = (x * a2 - y).abs().min((x * a1 + h - y).abs()); ans += tmp * tmp; } println!("{}", ans); }