Decision Framework: Which Library to Use

Each RAPIDS/GPU library, the CPU library it replaces, what it is good at, and when it is the wrong choice — CuPy, Numba CUDA, Warp, cuDF, cuML, cuGraph, KvikIO, cuxfilter, cuCIM, cuVS, cuSpatial, and RAFT — plus guidance on combining them.

Decision Framework: Which Library to Use

Choose the right tool based on what the user's code actually does. Read the appropriate reference file(s) before writing any GPU code.

CuPy — for array/matrix operations (NumPy replacement)

Read: references/cupy.md

Use CuPy when the user's code is primarily:

• NumPy array operations (element-wise math, linear algebra, FFT, sorting, reductions)
• SciPy operations (sparse matrices, signal processing, image filtering, special functions)
• Any code that chains NumPy calls — CuPy is a drop-in replacement

CuPy wraps NVIDIA's optimized libraries (cuBLAS, cuFFT, cuSOLVER, cuSPARSE, cuRAND) so standard operations are already tuned. Most NumPy code works by changing import numpy as np to import cupy as cp.

Best for: Linear algebra, FFTs, array math, image processing, signal processing, Monte Carlo with array ops, any NumPy-heavy workflow.

Numba CUDA — for custom GPU kernels

Read: references/numba.md

Use Numba when the user needs:

• Custom algorithms that don't map to standard array operations
• Fine-grained control over GPU threads, blocks, and shared memory
• Element-wise operations with complex logic (use @vectorize(target='cuda'))
• Reduction operations with custom logic
• Stencil computations or neighbor-dependent calculations
• Anything requiring the CUDA programming model directly

Numba compiles Python directly into CUDA kernels. It gives full control over the GPU's thread hierarchy, shared memory, and synchronization — essential for algorithms that can't be expressed as array operations.

Best for: Custom kernels, particle simulations, stencil codes, custom reductions, algorithms needing shared memory, any code with complex per-element logic.

Warp — for simulation, spatial computing, and differentiable programming

Read: references/warp.md

Use Warp when the user's code is primarily:

• Physics simulation (particles, cloth, fluids, rigid bodies, DEM, SPH)
• Geometry processing (mesh operations, ray casting, signed distance fields, marching cubes)
• Robotics (kinematics, dynamics, control with transforms and quaternions)
• Differentiable simulation for ML training (integrates with PyTorch/JAX autograd)
• Any Python simulation loop that needs to be JIT-compiled to GPU
• Spatial computing with meshes, volumes (NanoVDB), hash grids, or BVH queries

Warp JIT-compiles @wp.kernel Python functions to CUDA, with built-in types for spatial computing (vec3, mat33, quat, transform) and primitives for geometry queries (Mesh, Volume, HashGrid, BVH). All kernels are automatically differentiable. Note: the higher-level warp.sim module was removed in Warp 1.10 — its functionality moved to the separate Newton physics engine. Warp itself remains the right tool for writing custom simulation kernels.

Best for: Physics simulation, mesh ray casting, particle systems, differentiable rendering, robotics kinematics, SDF operations, any workload combining spatial data structures with GPU compute.

Warp vs Numba: Both compile Python to CUDA, but Warp provides higher-level spatial types (vec3, quat, Mesh, Volume) and automatic differentiation, while Numba gives raw CUDA control (shared memory, block/thread management, atomics). Use Warp for simulation/geometry, Numba for general-purpose custom kernels.

cuDF — for dataframe operations (pandas replacement)

Read: references/cudf.md

Use cuDF when the user's code is primarily:

• pandas DataFrame operations (filtering, groupby, joins, aggregations)
• CSV/Parquet/JSON reading and processing
• ETL pipelines or data wrangling on large datasets
• Any pandas-heavy workflow on datasets that fit in GPU memory

cuDF's cudf.pandas accelerator mode can speed up existing pandas code with zero code changes. For maximum performance, use the native cuDF API.

Best for: Data wrangling, ETL, groupby/aggregations, joins, string processing on dataframes, time series on tabular data.

cuML — for machine learning (scikit-learn replacement)

Read: references/cuml.md

Use cuML when the user's code is primarily:

• scikit-learn estimators (classification, regression, clustering, dimensionality reduction)
• ML preprocessing (scaling, encoding, imputation, feature extraction)
• Hyperparameter tuning or cross-validation
• Tree model inference (XGBoost, LightGBM, sklearn Random Forest via FIL)
• UMAP, t-SNE, HDBSCAN, or KNN on large datasets

cuML's cuml.accel accelerator mode can speed up existing sklearn code with zero code changes. For maximum performance, use the native cuML API. Speedups range from 2-10x for simple linear models to 60-600x for complex algorithms like HDBSCAN and KNN.

Best for: Classification, regression, clustering, dimensionality reduction, preprocessing pipelines, model inference, any scikit-learn-heavy workflow.

cuGraph — for graph analytics (NetworkX replacement)

Read: references/cugraph.md

Use cuGraph when the user's code is primarily:

• NetworkX graph algorithms (centrality, community detection, shortest paths, PageRank)
• Graph construction and analysis on large networks
• Social network analysis, knowledge graphs, or recommendation systems
• Any graph algorithm on networks with 10K+ edges

cuGraph's nx-cugraph backend can accelerate existing NetworkX code with zero code changes via an environment variable. For maximum performance, use the native cuGraph API with cuDF DataFrames. Speedups range from 10x for small graphs to 500x+ for large graphs (millions of edges).

Best for: PageRank, betweenness centrality, community detection (Louvain, Leiden), BFS/SSSP, connected components, link prediction, graph neural network sampling, any NetworkX-heavy workflow.

KvikIO — for high-performance GPU file IO

Read: references/kvikio.md

Use KvikIO when the user's code is primarily:

• Loading large binary data files directly into GPU memory
• Writing GPU arrays to disk without copying to host first
• Reading data from remote storage (S3, HTTP, WebHDFS) into GPU memory
• Working with Zarr arrays on GPU (GDSStore backend)
• Any pipeline where file IO is the bottleneck between storage and GPU

KvikIO provides Python bindings to NVIDIA cuFile, enabling GPUDirect Storage (GDS) — data flows directly between NVMe storage and GPU memory, bypassing CPU memory entirely. When GDS isn't available, it falls back to POSIX IO transparently. It handles both host and device data seamlessly.

Best for: Loading binary data to GPU, saving GPU arrays to disk, reading from S3/HTTP directly to GPU, Zarr arrays on GPU, replacing numpy.fromfile() → cupy patterns, any IO-heavy GPU pipeline where data staging through CPU memory is a bottleneck.

Note: For tabular formats (CSV, Parquet, JSON), use cuDF's built-in readers instead — they're optimized for those formats. KvikIO is for raw binary data and remote file access.

cuxfilter — for GPU-accelerated interactive dashboards

Read: references/cuxfilter.md

Project status: sunset. RAPIDS 26.06 was cuxfilter's final release (RSN 60) — the packages still work but receive no further updates. For new dashboards, prefer cuDF for GPU data prep combined with HoloViews/hvPlot/Datashader linked selections, served with Panel, Plotly Dash, Streamlit, or Bokeh. Reach for cuxfilter only when the user already uses it or explicitly asks for it.

Use cuxfilter when the user needs:

• Interactive cross-filtering dashboards on large datasets (millions of rows)
• Exploratory data analysis with linked charts that filter each other
• GPU-accelerated visualization with scatter plots, bar charts, heatmaps, choropleths, or graph visualizations
• Dashboard prototyping from Jupyter notebooks with minimal code
• Visualizing results from cuDF, cuML, or cuGraph pipelines

cuxfilter leverages cuDF for all data operations on the GPU — filtering, groupby, and aggregation happen entirely on the GPU, with only rendering results sent to the browser. It integrates Bokeh, Datashader (for millions of points), Deck.gl (for maps), and Panel widgets.

Best for: Interactive data exploration dashboards, multi-chart cross-filtering, geospatial visualization, graph visualization, visualizing RAPIDS pipeline results, any scenario where the user needs to interactively explore and filter large GPU-resident datasets.

cuCIM — for image processing (scikit-image replacement)

Read: references/cucim.md

Use cuCIM when the user's code is primarily:

• scikit-image operations (filtering, morphology, segmentation, feature detection, color conversion)
• Image preprocessing pipelines for deep learning (resize, normalize, augment)
• Digital pathology (whole-slide image reading, H&E stain normalization, cell counting)
• Microscopy, remote sensing, or medical imaging workflows
• Any scikit-image-heavy pipeline processing images at 512x512 or larger

cuCIM's cucim.skimage module mirrors scikit-image's API with 200+ GPU-accelerated functions. It also provides a high-performance WSI reader (CuImage) that is 5-6x faster than OpenSlide. All functions work on CuPy arrays — zero-copy, all on GPU.

Best for: Filtering (Gaussian, Sobel, Frangi), morphology, thresholding, connected component labeling, region properties, color space conversion, image registration, denoising, whole-slide image processing, DL preprocessing pipelines.

cuVS — for vector search (Faiss/Annoy replacement)

Read: references/cuvs.md

Use cuVS when the user's code is primarily:

• Approximate nearest neighbor (ANN) search on high-dimensional vectors
• Similarity search for RAG, recommender systems, or semantic retrieval
• k-NN graph construction for clustering or visualization
• Any Faiss, Annoy, ScaNN, or sklearn NearestNeighbors workload on large embedding datasets

cuVS provides GPU-accelerated ANN index types (CAGRA, IVF-Flat, IVF-PQ, brute force) plus HNSW for CPU serving from GPU-built indexes. It powers the GPU backends of Faiss, Milvus, and Lucene. Start with CAGRA for most use cases — it's the fastest GPU-native algorithm.

Best for: Embedding search, RAG retrieval, recommender systems, image/text/audio similarity search, k-NN graph construction, any nearest-neighbor workload on 10K+ vectors.

cuSpatial — for geospatial analytics (GeoPandas replacement)

Read: references/cuspatial.md

Project status: archived. The cuSpatial repository has been read-only since July 2025; the final release is 25.04, which pins cudf-cu12==25.4.* and therefore conflicts with current RAPIDS releases in the same environment. No official successor exists. Recommend it only in a dedicated legacy environment; otherwise keep geometry operations on GeoPandas/Shapely (CPU) and accelerate the tabular parts of the workflow with cuDF.

Use cuSpatial when the user's code is primarily:

• GeoPandas spatial operations (point-in-polygon, spatial joins, distance calculations)
• Trajectory analysis (grouping GPS traces, computing speeds/distances)
• Spatial indexing (quadtree) for large-scale spatial joins
• Haversine distance calculations on lat/lon coordinates
• Any GeoPandas/shapely-heavy workflow on large geospatial datasets

cuSpatial provides GPU-accelerated GeoSeries and GeoDataFrame types compatible with GeoPandas, plus spatial join, distance, and trajectory functions. Convert from GeoPandas with cuspatial.from_geopandas().

Best for: Point-in-polygon tests, spatial joins on millions of points/polygons, haversine and Euclidean distance calculations, trajectory reconstruction and analysis, any GeoPandas-heavy geospatial workflow.

RAFT (pylibraft) — for low-level GPU primitives and multi-GPU

Read: references/raft.md

Use RAFT when the user needs:

• GPU-accelerated sparse eigenvalue problems (scipy.sparse.linalg.eigsh replacement)
• Low-level GPU device memory management (device_ndarray)
• Random graph generation (R-MAT model for benchmarking)
• Multi-node multi-GPU communication infrastructure (via raft-dask)
• Building blocks that underlie higher-level RAPIDS libraries

RAFT provides the foundational primitives that cuML and cuGraph are built on. Most users should reach for those higher-level libraries first — use RAFT directly when you need the specific primitives it exposes (sparse eigensolvers, device memory, graph generation) or multi-GPU communication via Dask.

Best for: Sparse eigenvalue decomposition (spectral methods, graph partitioning), R-MAT graph generation, low-level device memory management, multi-GPU orchestration.

Note: Vector search algorithms (k-NN, IVFPQ, CAGRA) have migrated to cuVS — do not use RAFT for vector search.

Combining Libraries

Many real workloads benefit from using multiple libraries together. They interoperate via the CUDA Array Interface — zero-copy data sharing between CuPy, Numba, Warp, cuDF, cuML, cuGraph, cuVS, cuCIM, cuSpatial, KvikIO, PyTorch, JAX, and other GPU libraries.

Common combinations:

• cuDF + cuML: Load and preprocess data with cuDF, train/predict with cuML — the full RAPIDS pipeline
• cuDF + cuGraph: Build graphs from cuDF edge lists, run graph analytics with cuGraph
• cuGraph + cuML: Extract graph features with cuGraph, feed into cuML for ML
• cuML + cuVS: Train an embedding model with cuML, index and search embeddings with cuVS
• cuDF + CuPy: Load and filter data with cuDF, then do numerical analysis with CuPy
• CuPy + cuVS: Generate embeddings with CuPy operations, build a cuVS search index — zero-copy
• Warp + PyTorch: Differentiable simulation in Warp, backpropagate gradients into PyTorch training loop
• Warp + CuPy: Use CuPy for array math, Warp for spatial queries (mesh, volume) — zero-copy via CUDA Array Interface
• Warp + JAX: Warp kernels as JAX primitives inside jitted functions
• CuPy + Numba: Use CuPy for standard ops, drop into Numba for custom kernels
• cuDF + Numba: Process dataframes with cuDF, apply custom GPU functions via Numba UDFs
• cuML + CuPy: Train with cuML, do custom post-processing with CuPy
• cuDF + cuxfilter: Load data with cuDF, build interactive cross-filtering dashboards with cuxfilter
• cuML + cuxfilter: Run ML (e.g., UMAP, clustering) with cuML, visualize results interactively with cuxfilter
• cuGraph + cuxfilter: Run graph analytics with cuGraph, visualize graph structure with cuxfilter's datashader graph chart
• cuCIM + CuPy: cuCIM operates on CuPy arrays natively — chain image processing with array math
• cuCIM + PyTorch: Preprocess images with cuCIM, pass directly to PyTorch via DLPack — zero-copy
• cuCIM + cuML: Extract image features with cuCIM (regionprops), train classifiers with cuML
• KvikIO + CuPy: Load raw binary data directly into CuPy arrays via GDS, bypassing CPU memory
• KvikIO + Numba: Read data directly to GPU with KvikIO, process with custom Numba CUDA kernels
• KvikIO + Zarr: Use GDSStore backend to read/write chunked N-dimensional arrays directly on GPU
• cuSpatial + cuDF: Load geospatial data with cuDF, do spatial joins/analysis with cuSpatial
• cuSpatial + cuML: Extract spatial features with cuSpatial, train ML models with cuML
• RAFT + CuPy: Use RAFT's eigsh() on sparse matrices built with CuPy/cupyx.scipy.sparse
• RAFT + raft-dask: Scale GPU workloads across multiple GPUs/nodes via Dask