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⚡ Bolt: [KNN O(N) Selection] #119

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4 changes: 4 additions & 0 deletions .jules/bolt.md
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## 2026-05-01 - Avoid High-Level Tensor Ops in Scalar Reductions
**Learning:** High-level `Tensor` operations like `sub()` and `mul()` trigger intermediate heap allocations for shape and stride metadata. When computing scalar reductions (like MSE, distances, or loss functions), using these operations introduces severe memory overhead inside hot loops. Attempting to use `.min()` length truncation as a safeguard is an anti-pattern as it masks shape mismatch errors.
**Action:** For scalar reductions, assert shape equality (`assert_eq!(a.shape, b.shape)`) and perform a single-pass iteration directly over the underlying borrowed data arrays (`a.data.borrow()`) to eliminate intermediate allocations and safely compute the result.

## 2026-05-28 - O(N) Nearest Neighbor Selection
**Learning:** `KNNClassifier` uses a manual partial selection sort with $O(K \cdot N)$ complexity to find the $K$ nearest neighbors. This is highly inefficient in hot loops, especially when finding neighbors is a frequent operation. Finding $K$ nearest neighbors does not strictly require full sorting of the elements, only partitioning.
**Action:** Replace manual partial sorts with `select_nth_unstable_by` which provides $O(N)$ average time complexity. Use `partial_cmp().unwrap_or(core::cmp::Ordering::Equal)` to safely compare `f64` distances in the presence of `NaN` values without breaking the total ordering contract.
1 change: 0 additions & 1 deletion crates/aether-core/src/aether.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use libm::sqrt;
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1 change: 0 additions & 1 deletion crates/aether-core/src/governor.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

// use libm::fabs;
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1 change: 0 additions & 1 deletion crates/aether-core/src/lib.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![cfg_attr(not(feature = "std"), no_std)]

#[cfg(feature = "alloc")]
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1 change: 0 additions & 1 deletion crates/aether-core/src/manifold.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use libm::sqrt;
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1 change: 0 additions & 1 deletion crates/aether-core/src/memory.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#[cfg(not(feature = "std"))]
use alloc::boxed::Box;
#[cfg(not(feature = "std"))]
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/autograd.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#[cfg(not(feature = "std"))]
extern crate alloc;

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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/benchmark.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use crate::ml::convergence::{Answer, BettiNumbers, ConvergenceDetector, ResidualAnalyzer};
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14 changes: 6 additions & 8 deletions crates/aether-core/src/ml/classification.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

// use heapless::Vec as HVec;
Expand Down Expand Up @@ -203,13 +202,12 @@ impl<const D: usize> KNNClassifier<D> {
*dist = (self.distance(x, &self.x_train[i]), self.y_train[i]);
}

// Sort by distance (simple bubble sort for small k)
for i in 0..self.k.min(self.n_train) {
for j in (i + 1)..self.n_train {
if distances[j].0 < distances[i].0 {
distances.swap(i, j);
}
}
// Select k nearest neighbors (O(N) on average)
let k_min = self.k.min(self.n_train);
if k_min > 0 {
distances[..self.n_train].select_nth_unstable_by(k_min - 1, |a, b| {
a.0.partial_cmp(&b.0).unwrap_or(core::cmp::Ordering::Equal)
});
}

// Vote among k nearest
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/clustering.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use libm::{fabs, sqrt};
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/convergence.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use heapless::Vec as HVec;
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/convolution.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use crate::ml::neural::Activation;
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/gossip.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use crate::ml::clustering::{KMeans, KMeansResult};
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/linalg.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

#[cfg(feature = "alloc")]
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/mod.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

// Core modules
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/neural.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

#[cfg(feature = "alloc")]
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/regressor.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

use heapless::Vec as HVec;
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1 change: 0 additions & 1 deletion crates/aether-core/src/ml/tensor.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#[cfg(feature = "alloc")]
use alloc::rc::Rc;
#[cfg(feature = "alloc")]
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1 change: 0 additions & 1 deletion crates/aether-core/src/os.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


/// CPU Register Context
///
/// This structure represents the state of the CPU registers. It is used for:
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1 change: 0 additions & 1 deletion crates/aether-core/src/state.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


use core::ops::Sub;
use libm::sqrt;

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1 change: 0 additions & 1 deletion crates/aether-core/src/topology.rs
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// ═══════════════════════════════════════════════════════════════════════════════
//


#![allow(dead_code)]

// use libm::fabs;
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