GSOC 2026: New function pgr_coreNumbers to be added in pgRouting

[sakirr05]

pgr_coreNumbers():

coreNumbers(): K-core decomposition is an algorithm that assigns to every vertex its core number: the largest value of k for which the vertex still belongs to the k-core of the graph. The k-core is the maximal subgraph in which every vertex has degree at least k within that subgraph. The decomposition repeatedly peels away vertices whose degree falls below k, raising k at each stage until no vertices remain. Core numbers measure how deeply a vertex sits in the dense part of a network: on a road network core 1 marks dead-ends and cul-de-sacs, core 2 marks corridors and cycles, and core 3 and above mark densely interconnected regions with redundant routes. This implementation follows the Batagelj-Zaversnik peeling algorithm with a time complexity of O(E) and space complexity of O(V), where V is the number of vertices and E is the number of edges. This will enhance pgRouting's capabilities in network resilience and graph degeneracy analysis.

The algorithm:

• Works on undirected graphs.
• Edge direction and traversal costs are ignored, only the edge endpoints matter.
• Collapses parallel edges before peeling, so edge multiplicity does not inflate core numbers.
• Drops self loops before peeling, as a vertex is not its own neighbour.
• Returns every vertex of the graph, so the result has |V| rows.
• Running time: O(E) where E is the number of edges.

Signature:

• pgr_coreNumbers()

pgr_coreNumbers(Edges SQL)

Returns set of (seq, node, core)
OR EMPTY SET

Parameters

Parameter	Type	Description
Edges SQL	TEXT	Inner SQL query, as described below.

Inner Query

Edges SQL: An SQL query returning a set of rows with the following columns:

Column	Type	Default	Description
id	ANY-INTEGER		Identifier of the edge.
source	ANY-INTEGER		Identifier of the first endpoint vertex of the edge.
target	ANY-INTEGER		Identifier of the second endpoint vertex of the edge.
cost	ANY-NUMERICAL		Weight of the edge (source, target). When negative, the edge does not exist.
reverse_cost	ANY-NUMERICAL	-1	Weight of the edge (target, source). When negative, the edge does not exist.

Where:

• ANY-INTEGER = SMALLINT, INTEGER, BIGINT
• ANY-NUMERICAL = SMALLINT, INTEGER, BIGINT, REAL, FLOAT

Result Columns

Returns SETOF (seq, node, core).

Column	Type	Description
seq	BIGINT	Sequential value starting from 1.
node	BIGINT	Identifier of the vertex.
core	BIGINT	Core number of the vertex: the largest k for which the vertex belongs to the k-core.