| |
| use hyperkitty_core::{GOLDEN_RATIO_INV, GOLDEN_RATIO_INV_SQ}; |
|
|
| #[derive(Debug, Clone)] |
| pub struct DensityMatrix { |
| pub data: Vec<Vec<f64>>, |
| } |
|
|
| impl DensityMatrix { |
| pub fn new(n: usize) -> Self { |
| Self { data: vec![vec![0.0; n]; n] } |
| } |
|
|
| pub fn identity(n: usize) -> Self { |
| let mut d = Self::new(n); |
| for i in 0..n { |
| d.data[i][i] = 1.0; |
| } |
| d |
| } |
|
|
| pub fn size(&self) -> usize { |
| self.data.len() |
| } |
|
|
| pub fn multiply(&self, other: &Self) -> Self { |
| let n = self.size(); |
| let mut result = Self::new(n); |
| for i in 0..n { |
| for j in 0..n { |
| let mut sum = 0.0; |
| for k in 0..n { |
| sum += self.data[i][k] * other.data[k][j]; |
| } |
| result.data[i][j] = sum; |
| } |
| } |
| result |
| } |
|
|
| pub fn scale(&self, s: f64) -> Self { |
| let mut result = self.clone(); |
| for row in &mut result.data { |
| for val in row { |
| *val *= s; |
| } |
| } |
| result |
| } |
|
|
| pub fn add(&self, other: &Self) -> Self { |
| let n = self.size(); |
| let mut result = Self::new(n); |
| for i in 0..n { |
| for j in 0..n { |
| result.data[i][j] = self.data[i][j] + other.data[i][j]; |
| } |
| } |
| result |
| } |
|
|
| pub fn transpose(&self) -> Self { |
| let n = self.size(); |
| let mut result = Self::new(n); |
| for i in 0..n { |
| for j in 0..n { |
| result.data[i][j] = self.data[j][i]; |
| } |
| } |
| result |
| } |
|
|
| pub fn evolve(&self, u: &Self) -> Self { |
| let ut = u.transpose(); |
| let urho = u.multiply(self); |
| let urhou = urho.multiply(&ut); |
| let term1 = urhou.scale(GOLDEN_RATIO_INV); |
| let term2 = self.scale(GOLDEN_RATIO_INV_SQ); |
| term1.add(&term2) |
| } |
|
|
| pub fn frobenius_norm(&self) -> f64 { |
| self.data.iter().flat_map(|row| row).map(|x| x * x).sum::<f64>().sqrt() |
| } |
|
|
| pub fn distance_to(&self, other: &Self) -> f64 { |
| self.add(&other.scale(-1.0)).frobenius_norm() |
| } |
|
|
| pub fn trace(&self) -> f64 { |
| let n = self.size(); |
| (0..n).map(|i| self.data[i][i]).sum() |
| } |
| } |
|
|
| #[cfg(test)] |
| mod tests { |
| use super::*; |
|
|
| #[test] |
| fn identity_trace() { |
| let id = DensityMatrix::identity(3); |
| assert!((id.trace() - 3.0).abs() < 1e-10); |
| } |
| } |
|
|
