feat: add lazy normalization for Lasso and Elastic Net

.github/workflows/ci.yml

@@ -57,6 +57,8 @@ jobs:
           - "--features serde"
           - "--features datasets"
           - "--features ndarray-bindings"
+          - "--features lazy-normalization"
+          - "--features lazy-normalization,ndarray-bindings"
           - ""
     steps:
       - uses: actions/checkout@v4
@@ -73,7 +75,7 @@ jobs:
       - name: Stable Build
         run: cargo build --no-default-features ${{ matrix.features }}
       - name: Tests
-        if: matrix.features == '--features ndarray-bindings'
+        if: matrix.features == '--features ndarray-bindings' || contains(matrix.features, 'lazy-normalization')
         run: cargo test --no-default-features ${{ matrix.features }}
 
   msrv:

CHANGELOG.md

@@ -5,6 +5,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Added
+- Optional `lazy-normalization` support for Lasso and Elastic Net. It applies normalization to a borrowed design and keeps Elastic Net's identity-block augmentation implicit, while retaining the dense Gram workspace. Enable the feature and set `with_lazy_normalization(true)` to select this path. The default remains eager. The new parameter field is available only with the feature and defaults to false during deserialization (#479).
+
+### Changed
+- **Breaking change:** Enabling `lazy-normalization` adds a public `lazy_normalization` field to `LassoParameters`, `LassoSearchParameters`, `ElasticNetParameters`, and `ElasticNetSearchParameters`. Struct literals without `..Default::default()` must add `lazy_normalization: false` to retain the eager path, or `true` to select the lazy path. This also applies when another dependency enables the feature through Cargo feature unification (#479).
 
 ## [0.6.16]
 ### Fixed

Cargo.toml

@@ -24,6 +24,7 @@ exclude = [
 [dependencies]
 approx = "0.5.1"
 cfg-if = "1.0.0"
+lazymatrix = { version = "0.6.0", optional = true, default-features = false }
 ndarray = { version = "0.17", optional = true }
 num-traits = "0.2.12"
 num = "0.4"
@@ -46,6 +47,9 @@ serde = ["dep:serde", "dep:typetag"]
 # Optional bindings for the ndarray crate (DenseMatrix <-> ndarray).
 ndarray-bindings = ["dep:ndarray"]
 
+# Apply Lasso and Elastic Net normalization without copying the design matrix.
+lazy-normalization = ["dep:lazymatrix"]
+
 # Sample datasets (iris, boston, digits, ...) and dataset generators.
 # Enables std_rand and serde because datasets ship serialized bundles.
 datasets = ["std_rand", "serde"]

README.md

@@ -100,6 +100,29 @@ smartcore organizes algorithms into clear modules with consistent traits:
 
 Recent refactors emphasize reusable components in trees/forests and expanded multiclass SVM capabilities. XGBoost-style regression and single-linkage clustering have been added. See CHANGELOG for API changes and migration notes.
 
+## Optional lazy normalization
+
+The optional `lazy-normalization` feature lets Lasso and Elastic Net borrow the
+design matrix during normalization. Elastic Net also applies its identity-block
+augmentation without storing the augmented design. Enable it with `features =
+["lazy-normalization"]`, then select it with
+`LassoParameters::default().with_lazy_normalization(true)` or
+`ElasticNetParameters::default().with_lazy_normalization(true)`. The default
+remains eager, even when the feature is enabled. The `normalize` option still
+controls whether columns are centered and scaled. Parameter searches use the
+fixed `lazy_normalization` setting. It works with `DenseMatrix` and
+`ndarray-bindings`.
+
+Lazy normalization reduces memory use by computing normalized values when the
+solver needs them. This adds repeated arithmetic and can increase fit time for
+both estimators, including Elastic Net on large inputs. The solver still stores
+a dense Gram matrix with one row and column per feature.
+
+Enabling the feature adds a public `lazy_normalization` field to both estimators'
+parameter and search parameter structs. Code that constructs these structs
+without `..Default::default()` must add the field. Missing fields default to
+`false` during deserialization.
+
 ## Data access and readers
 
 - CSV readers: Read matrices from CSV with configurable delimiter and header rows, with helpful error messages and testing utilities (including non-IO reader abstractions).