Core Number

SQL function: cugraph_core_number

Official cuGraph reference: C API

Assign each vertex the largest k for which it belongs to a k-core, where every vertex has degree at least k within that subgraph.

Signature

cugraph_core_number(table_name [, src_col, dst_col [, weight_col [, options_json]]])

Relation inputs

The first positional argument names a registered edge table or view (the edges role). Parenthesized relation subqueries are not accepted; metadata validation uses the same registered name.

Vertex ID types

The edges relation declares the accepted vertex-ID domains. Numeric calls preserve the existing numeric schema. When logical string support is declared, Utf8, LargeUtf8, and Utf8View endpoint columns share one logical domain; their vertex-identity outputs are canonicalized to Utf8.

Domain	Accepted endpoint inputs	Output contract
Numeric edge endpoints	Int32, Int64	The numeric output schema is used for numeric calls.
Logical string edge endpoints	Utf8, LargeUtf8, Utf8View	Vertex identity columns are canonicalized to Utf8; scores, distances, counts, coordinates, and opaque labels remain numeric.

The native mapping type is Int64. Call-specific output schemas come from gpu_validate_call.

Logical string side-input limitations:

• edge ID columns and edge-ID predicate side inputs are not supported for logical string graphs

Scalar arguments & JSON options

Positional scalar arguments

src_col and dst_col name the edge endpoint columns; both are optional and default to src and dst.

Argument	Type	Required	Default	Notes
weight_col	Utf8|null	no		accepted as an edge-column binding; native algorithm execution does not consume weights; semantic effect: none for this algorithm

JSON options

Option	Type	Default	Constraints	Description
degree_type	Utf8	"in_out"	one of "in", "out", "in_out"

Graph construction options

This function builds an undirected graph by default (directed=false); all other graph construction options follow the shared defaults documented in Graph Construction Options.

Output schema

Column	Type	Nullable	Description
vertex	Int64|Utf8	no	Vertex whose core number is reported.
core_number	Int64	no	Largest k value for which the vertex belongs to the graph k-core.

These are generic descriptor schemas; validate the call to get the concrete, table-specific output schema.

Examples

This example runs on the citation network demo dataset.

Find the densest citation core

Core number measures how deep a vertex sits in recursively denser subgraphs (with degree_type: "in_out", degree is in + out). Define the result as a workspace view, find the deepest shell, and list its members:

CREATE VIEW cores AS
SELECT vertex, core_number FROM cugraph_core_number('citation_edges', 'src', 'dst');

SELECT MAX(core_number) AS deepest,
       COUNT(*) FILTER (WHERE core_number = 70) AS members
FROM cores;

deepest	members
70	5,913

SELECT p.year, p.title
FROM cores c JOIN papers p ON p.paper_id = c.vertex
WHERE c.core_number = 70
ORDER BY p.n_citation DESC
LIMIT 6;

year	title
2004	Distinctive Image Features from Scale-Invariant Keypoints
2001	Random Forests
2011	LIBSVM: A library for support vector machines
1995	The Nature of Statistical Learning Theory
1995	Support-Vector Networks
1986	A Computational Approach to Edge Detection

The 70-core — 5,913 papers, each with at least 70 combined in/out edges to other members of the shell — is recognizably the machine-learning and computer-vision literature.

Limitations & lifecycle

No algorithm-specific limitations.

Validate before running

Dry-run validation checks registered relation metadata, column presence, static dtypes, and options only; it does not scan edge data, construct a graph, or prove source-vertex existence:

SELECT * FROM gpu_validate_call(
  'cugraph_core_number',
  '{"schema_version":1,"relations":{"edges":{"table":"target_edges"}},"options":{"src_col":"src","dst_col":"dst"}}'
);

See GPU Function Catalog API for the full gpu_validate_call contract.