avila-clustering 0.1.0

//! Spectral clustering

use crate::{ClusteringError, Result};
use ndarray::{Array1, Array2, ArrayView2};

/// Affinity type for spectral clustering
#[derive(Debug, Clone)]
pub enum AffinityType {
    /// Precomputed affinity matrix
    Precomputed,
    /// Nearest neighbors graph
    NearestNeighbors { n_neighbors: usize },
    /// RBF kernel
    RBF { gamma: f64 },
}

/// Eigen solver for spectral clustering
#[derive(Debug, Clone, Copy)]
pub enum EigenSolver {
    /// ARPACK solver
    Arpack,
    /// Locally Optimal Block Preconditioned Conjugate Gradient
    Lobpcg,
    /// Dense solver
    Dense,
}

/// Label assignment method
#[derive(Debug, Clone, Copy)]
pub enum AssignMethod {
    /// Use KMeans on embeddings
    KMeans,
    /// Discretize eigenvectors
    Discretize,
}

/// Spectral clustering
pub struct SpectralClustering {
    n_clusters: usize,
    affinity: AffinityType,
    eigen_solver: EigenSolver,
    assign_labels: AssignMethod,
}

impl SpectralClustering {
    pub fn builder(n_clusters: usize) -> SpectralClusteringBuilder {
        SpectralClusteringBuilder::new(n_clusters)
    }

    pub fn new(n_clusters: usize) -> Self {
        Self::builder(n_clusters).build()
    }

    pub fn fit_predict(&self, data: &ArrayView2<f64>) -> Result<Array1<usize>> {
        // TODO: Implement spectral clustering
        // 1. Construct affinity matrix
        // 2. Compute normalized Laplacian
        // 3. Compute eigenvectors
        // 4. Assign labels using KMeans or discretization
        unimplemented!("SpectralClustering::fit_predict")
    }
}

pub struct SpectralClusteringBuilder {
    n_clusters: usize,
    affinity: AffinityType,
    eigen_solver: EigenSolver,
    assign_labels: AssignMethod,
}

impl SpectralClusteringBuilder {
    pub fn new(n_clusters: usize) -> Self {
        Self {
            n_clusters,
            affinity: AffinityType::RBF { gamma: 1.0 },
            eigen_solver: EigenSolver::Arpack,
            assign_labels: AssignMethod::KMeans,
        }
    }

    pub fn affinity(mut self, affinity: AffinityType) -> Self {
        self.affinity = affinity;
        self
    }

    pub fn eigen_solver(mut self, solver: EigenSolver) -> Self {
        self.eigen_solver = solver;
        self
    }

    pub fn assign_labels(mut self, method: AssignMethod) -> Self {
        self.assign_labels = method;
        self
    }

    pub fn build(self) -> SpectralClustering {
        SpectralClustering {
            n_clusters: self.n_clusters,
            affinity: self.affinity,
            eigen_solver: self.eigen_solver,
            assign_labels: self.assign_labels,
        }
    }
}