Overview of Graph Reduction Functions

Table of Contents

• What is a Graph Vertex Reduction?
• Function Categories
  • Const vs. Non-Const Graph
  • Basic vs. WithArgument Variants
  • Scope and Conditional Variants (Which Vertices to Process)
• Complete Function Graph
  • Basic Reduction Functions
  • WithArgument Reduction Functions
• Common Parameters
• Related Pages

This page provides an overview of all reduction functions available for graph operations, helping to understand the differences between variants and choose the right function for your needs.

What is a Graph Vertex Reduction?

A graph vertex reduction performs a reduction operation (like sum, max, min) across the edges connected to each vertex of a graph, producing one result per vertex. This is a fundamental operation for:

• computation of vertex degrees,
• finding maximum/minimum edge weights connected to each vertex,
• vertex-level statistics and analysis
• algorithms like PageRank, centrality measures, etc.

Function Categories

Graph reduction functions are organized along three independent axes:

Const vs. Non-Const Graph

Category	Graph Modifiable?	Use Case
Non-const	Yes	Can modify graph edges during reduction
Const	No	Read-only access to graph edges

Note: Each reduction function has both const and non-const overloads. The possibility to modify the graph during reduction allows to fuse reduction with traversing operations into a single pass. This can improve performance by reducing memory accesses.

Basic vs. WithArgument Variants

Category	Tracks Position?	Use Case
Basic	No	Only the reduced weight is needed (e.g., vertex sum, vertex max)
WithArgument	Yes	Need weight and target vertex index (e.g., max weight location)

Scope and Conditional Variants (Which Vertices to Process)

Scope	Vertices Processed	Parameters
All	All vertices	No range/array parameters
Range	Vertices [begin, end)	begin and end indices
Array	Specific vertices	Array of vertex indices
If	Vertices filtered by a condition	Process vertices based on vertex-level properties

Complete Function Graph

All reduction functions follow this naming pattern: reduce[All]Vertices[WithArgument][If]

Each function has both const and non-const overloads (×2 multiplier).

Basic Reduction Functions

Function	Scope	Conditional	Tracks Position	Overloads
reduceAllVertices	All	No	No	const & non-const
reduceVertices (range)	Range [begin,end)	No	No	const & non-const
reduceVertices (array)	Vertex array	No	No	const & non-const
reduceAllVerticesIf	All	Yes	No	const & non-const
reduceVerticesIf	Range [begin,end)	Yes	No	const & non-const

WithArgument Reduction Functions

Function	Scope	Conditional	Tracks Position	Overloads
reduceAllVerticesWithArgument	All	No	Yes	const & non-const
reduceVerticesWithArgument (range)	Range [begin,end)	No	Yes	const & non-const
reduceVerticesWithArgument (array)	Vertex array	No	Yes	const & non-const
reduceAllVerticesWithArgumentIf	All	Yes	Yes	const & non-const
reduceVerticesWithArgumentIf	Range [begin,end)	Yes	Yes	const & non-const

Common Parameters

All reduction functions share these common parameters:

• graph: The graph to reduce (const or non-const)
• fetch: Lambda that retrieves edge weights (see For Non-Const Graphs or For Const Graphs)
• reduction: Lambda or function object that combines weights (see Basic Reduction (Without Arguments) or Reduction With Argument (Position Tracking))
• store: Lambda that stores the reduction results (see Basic Store (Vertex Index Only) or variants)
• identity: The identity edge for the reduction (e.g., 0 for addition, 1 for multiplication)
• launchConfig: Configuration for parallel execution (optional)

Additional parameters:

• Scope variants: begin, end (range) or vertexIndexes (array)
• If variants: condition lambda for vertex filtering (see Condition Check)

Related Pages

• Graph Reduction Lambda Function Reference - Detailed lambda function signatures
• Overview of Graph Traversal Functions - Graph traversal operations