PCA preprocessor (#1808)

Resolves #1207. Depends on NVIDIA/raft#2952
This PR introduces the `cuvs::preprocessing::pca` with `float` support. The following APIs are supported:
`fit`, `transform`, `fit_transform`, `inverse_transform`.

Authors:
  - Anupam (https://github.com/aamijar)
  - Divye Gala (https://github.com/divyegala)

Approvers:
  - Divye Gala (https://github.com/divyegala)

URL: #1808

Author: aamijar

cpp/CMakeLists.txt

@@ -664,6 +664,7 @@ if(NOT BUILD_CPU_ONLY)
     src/preprocessing/quantize/binary.cu
     src/preprocessing/quantize/pq.cu
     src/preprocessing/spectral/spectral_embedding.cu
+    src/preprocessing/pca/pca.cu
     src/selection/select_k_float_int64_t.cu
     src/selection/select_k_float_int32_t.cu
     src/selection/select_k_float_uint32_t.cu

cpp/include/cuvs/preprocessing/pca.hpp

@@ -0,0 +1,185 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <raft/core/device_mdspan.hpp>
+#include <raft/core/resources.hpp>
+#include <raft/linalg/pca_types.hpp>
+
+namespace cuvs::preprocessing::pca {
+
+using solver = raft::linalg::solver;
+
+/**
+ * @brief Parameters for PCA decomposition. Ref:
+ * http://scikit-learn.org/stable/modules/generated/sklearn.decomposition.PCA.html
+ */
+struct params {
+  /** @brief Number of components to keep. */
+  int n_components = 1;
+
+  /**
+   * @brief If false, data passed to fit are overwritten and running fit(X).transform(X) will
+   * not yield the expected results, use fit_transform(X) instead.
+   */
+  bool copy = true;
+
+  /**
+   * @brief When true (false by default) the components vectors are multiplied by the square
+   * root of n_samples and then divided by the singular values to ensure uncorrelated outputs with
+   * unit component-wise variances.
+   */
+  bool whiten = false;
+
+  /** @brief The solver algorithm to use. */
+  solver algorithm = solver::COV_EIG_DQ;
+
+  /**
+   * @brief Tolerance for singular values computed by svd_solver == 'arpack' or
+   * the Jacobi solver.
+   */
+  float tol = 0.0f;
+
+  /**
+   * @brief Number of iterations for the power method computed by the Jacobi solver.
+   */
+  int n_iterations = 15;
+};
+
+/**
+ * @defgroup pca PCA (Principal Component Analysis)
+ * @{
+ */
+
+/**
+ * @brief Perform PCA fit operation.
+ *
+ * Computes the principal components, explained variances, singular values, and column means
+ * from the input data.
+ *
+ * @code{.cpp}
+ * #include <raft/core/resources.hpp>
+ * #include <cuvs/preprocessing/pca.hpp>
+ *
+ * raft::resources handle;
+ *
+ * cuvs::preprocessing::pca::params params;
+ * params.n_components = 2;
+ *
+ * auto input = raft::make_device_matrix<float, int>(handle, n_rows, n_cols);
+ * // ... fill input ...
+ *
+ * auto components       = raft::make_device_matrix<float, int, raft::col_major>(
+ *     handle, params.n_components, n_cols);
+ * auto explained_var    = raft::make_device_vector<float, int>(handle, params.n_components);
+ * auto explained_var_ratio = raft::make_device_vector<float, int>(handle, params.n_components);
+ * auto singular_vals    = raft::make_device_vector<float, int>(handle, params.n_components);
+ * auto mu               = raft::make_device_vector<float, int>(handle, n_cols);
+ * auto noise_vars       = raft::make_device_scalar<float>(handle);
+ *
+ * cuvs::preprocessing::pca::fit(handle, params,
+ *     input.view(), components.view(), explained_var.view(),
+ *     explained_var_ratio.view(), singular_vals.view(), mu.view(), noise_vars.view());
+ * @endcode
+ *
+ * @param[in] handle raft resource handle
+ * @param[in] config PCA parameters
+ * @param[inout] input input data [n_rows x n_cols] (col-major). Modified temporarily.
+ * @param[out] components principal components [n_components x n_cols] (col-major)
+ * @param[out] explained_var explained variances [n_components]
+ * @param[out] explained_var_ratio explained variance ratios [n_components]
+ * @param[out] singular_vals singular values [n_components]
+ * @param[out] mu column means [n_cols]
+ * @param[out] noise_vars noise variance (scalar)
+ * @param[in] flip_signs_based_on_U whether to determine signs by U (true) or V.T (false)
+ */
+void fit(raft::resources const& handle,
+         const params& config,
+         raft::device_matrix_view<float, int64_t, raft::col_major> input,
+         raft::device_matrix_view<float, int64_t, raft::col_major> components,
+         raft::device_vector_view<float, int64_t> explained_var,
+         raft::device_vector_view<float, int64_t> explained_var_ratio,
+         raft::device_vector_view<float, int64_t> singular_vals,
+         raft::device_vector_view<float, int64_t> mu,
+         raft::device_scalar_view<float, int64_t> noise_vars,
+         bool flip_signs_based_on_U = false);
+
+/**
+ * @brief Perform PCA fit and transform operations.
+ *
+ * Computes the principal components and transforms the input data into the eigenspace
+ * in a single operation.
+ *
+ * @param[in] handle raft resource handle
+ * @param[in] config PCA parameters
+ * @param[inout] input input data [n_rows x n_cols] (col-major). Modified temporarily.
+ * @param[out] trans_input transformed data [n_rows x n_components] (col-major)
+ * @param[out] components principal components [n_components x n_cols] (col-major)
+ * @param[out] explained_var explained variances [n_components]
+ * @param[out] explained_var_ratio explained variance ratios [n_components]
+ * @param[out] singular_vals singular values [n_components]
+ * @param[out] mu column means [n_cols]
+ * @param[out] noise_vars noise variance (scalar)
+ * @param[in] flip_signs_based_on_U whether to determine signs by U (true) or V.T (false)
+ */
+void fit_transform(raft::resources const& handle,
+                   const params& config,
+                   raft::device_matrix_view<float, int64_t, raft::col_major> input,
+                   raft::device_matrix_view<float, int64_t, raft::col_major> trans_input,
+                   raft::device_matrix_view<float, int64_t, raft::col_major> components,
+                   raft::device_vector_view<float, int64_t> explained_var,
+                   raft::device_vector_view<float, int64_t> explained_var_ratio,
+                   raft::device_vector_view<float, int64_t> singular_vals,
+                   raft::device_vector_view<float, int64_t> mu,
+                   raft::device_scalar_view<float, int64_t> noise_vars,
+                   bool flip_signs_based_on_U = false);
+
+/**
+ * @brief Perform PCA transform operation.
+ *
+ * Transforms the input data into the eigenspace using previously computed principal components.
+ *
+ * @param[in] handle raft resource handle
+ * @param[in] config PCA parameters
+ * @param[inout] input data to transform [n_rows x n_cols] (col-major). Modified temporarily
+ * (mean-centered then restored).
+ * @param[in] components principal components [n_components x n_cols] (col-major)
+ * @param[in] singular_vals singular values [n_components]
+ * @param[in] mu column means [n_cols]
+ * @param[out] trans_input transformed data [n_rows x n_components] (col-major)
+ */
+void transform(raft::resources const& handle,
+               const params& config,
+               raft::device_matrix_view<float, int64_t, raft::col_major> input,
+               raft::device_matrix_view<float, int64_t, raft::col_major> components,
+               raft::device_vector_view<float, int64_t> singular_vals,
+               raft::device_vector_view<float, int64_t> mu,
+               raft::device_matrix_view<float, int64_t, raft::col_major> trans_input);
+
+/**
+ * @brief Perform PCA inverse transform operation.
+ *
+ * Transforms data from the eigenspace back to the original space.
+ *
+ * @param[in] handle raft resource handle
+ * @param[in] config PCA parameters
+ * @param[in] trans_input transformed data [n_rows x n_components] (col-major)
+ * @param[in] components principal components [n_components x n_cols] (col-major)
+ * @param[in] singular_vals singular values [n_components]
+ * @param[in] mu column means [n_cols]
+ * @param[out] output reconstructed data [n_rows x n_cols] (col-major)
+ */
+void inverse_transform(raft::resources const& handle,
+                       const params& config,
+                       raft::device_matrix_view<float, int64_t, raft::col_major> trans_input,
+                       raft::device_matrix_view<float, int64_t, raft::col_major> components,
+                       raft::device_vector_view<float, int64_t> singular_vals,
+                       raft::device_vector_view<float, int64_t> mu,
+                       raft::device_matrix_view<float, int64_t, raft::col_major> output);
+
+/** @} */  // end group pca
+
+}  // namespace cuvs::preprocessing::pca

cpp/src/preprocessing/pca/detail/pca.cuh

@@ -0,0 +1,109 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <cuvs/preprocessing/pca.hpp>
+
+#include <raft/core/device_mdspan.hpp>
+#include <raft/core/resources.hpp>
+#include <raft/linalg/pca.cuh>
+
+namespace cuvs::preprocessing::pca::detail {
+
+/**
+ * @brief Convert cuvs::preprocessing::pca::params to raft::linalg::paramsPCA.
+ */
+inline auto to_raft_params(const params& config) -> raft::linalg::paramsPCA
+{
+  raft::linalg::paramsPCA prms;
+  prms.algorithm    = config.algorithm;
+  prms.tol          = config.tol;
+  prms.n_iterations = config.n_iterations;
+  prms.copy         = config.copy;
+  prms.whiten       = config.whiten;
+  return prms;
+}
+
+template <typename DataT, typename IndexT>
+void fit(raft::resources const& handle,
+         const params& config,
+         raft::device_matrix_view<DataT, IndexT, raft::col_major> input,
+         raft::device_matrix_view<DataT, IndexT, raft::col_major> components,
+         raft::device_vector_view<DataT, IndexT> explained_var,
+         raft::device_vector_view<DataT, IndexT> explained_var_ratio,
+         raft::device_vector_view<DataT, IndexT> singular_vals,
+         raft::device_vector_view<DataT, IndexT> mu,
+         raft::device_scalar_view<DataT, IndexT> noise_vars,
+         bool flip_signs_based_on_U)
+{
+  auto raft_prms = to_raft_params(config);
+  raft::linalg::pca_fit(handle,
+                        raft_prms,
+                        input,
+                        components,
+                        explained_var,
+                        explained_var_ratio,
+                        singular_vals,
+                        mu,
+                        noise_vars,
+                        flip_signs_based_on_U);
+}
+
+template <typename DataT, typename IndexT>
+void fit_transform(raft::resources const& handle,
+                   const params& config,
+                   raft::device_matrix_view<DataT, IndexT, raft::col_major> input,
+                   raft::device_matrix_view<DataT, IndexT, raft::col_major> trans_input,
+                   raft::device_matrix_view<DataT, IndexT, raft::col_major> components,
+                   raft::device_vector_view<DataT, IndexT> explained_var,
+                   raft::device_vector_view<DataT, IndexT> explained_var_ratio,
+                   raft::device_vector_view<DataT, IndexT> singular_vals,
+                   raft::device_vector_view<DataT, IndexT> mu,
+                   raft::device_scalar_view<DataT, IndexT> noise_vars,
+                   bool flip_signs_based_on_U)
+{
+  auto raft_prms = to_raft_params(config);
+  raft::linalg::pca_fit_transform(handle,
+                                  raft_prms,
+                                  input,
+                                  trans_input,
+                                  components,
+                                  explained_var,
+                                  explained_var_ratio,
+                                  singular_vals,
+                                  mu,
+                                  noise_vars,
+                                  flip_signs_based_on_U);
+}
+
+template <typename DataT, typename IndexT>
+void transform(raft::resources const& handle,
+               const params& config,
+               raft::device_matrix_view<DataT, IndexT, raft::col_major> input,
+               raft::device_matrix_view<DataT, IndexT, raft::col_major> components,
+               raft::device_vector_view<DataT, IndexT> singular_vals,
+               raft::device_vector_view<DataT, IndexT> mu,
+               raft::device_matrix_view<DataT, IndexT, raft::col_major> trans_input)
+{
+  auto raft_prms = to_raft_params(config);
+  raft::linalg::pca_transform(handle, raft_prms, input, components, singular_vals, mu, trans_input);
+}
+
+template <typename DataT, typename IndexT>
+void inverse_transform(raft::resources const& handle,
+                       const params& config,
+                       raft::device_matrix_view<DataT, IndexT, raft::col_major> trans_input,
+                       raft::device_matrix_view<DataT, IndexT, raft::col_major> components,
+                       raft::device_vector_view<DataT, IndexT> singular_vals,
+                       raft::device_vector_view<DataT, IndexT> mu,
+                       raft::device_matrix_view<DataT, IndexT, raft::col_major> output)
+{
+  auto raft_prms = to_raft_params(config);
+  raft::linalg::pca_inverse_transform(
+    handle, raft_prms, trans_input, components, singular_vals, mu, output);
+}
+
+}  // namespace cuvs::preprocessing::pca::detail