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100 changes: 100 additions & 0 deletions algorithms/bfs.md
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---
title: "BFS"
description: "BFS"
---

# BFS

## Overview

The Breadth-First Search (BFS) procedure allows you to perform a breadth-first traversal of a graph starting from a specific node.
BFS explores all the nodes at the present depth before moving on to nodes at the next depth level.
This is particularly useful for finding the shortest path between two nodes or exploring a graph layer by layer.

## Syntax

```
CALL algo.bfs(start_node, max_depth, relationship)
YIELD nodes, edges
```

## Arguments

| Name | Type | Description | Default |
|--------------|----------------|-----------------------------------------------------------------------------|------------|
| start_node | Node | Starting node for the BFS traversal | (Required) |
| max_depth | Integer | Maximum depth to traverse | (Required) |
| relationship | String or null | The relationship type to traverse. If null, all relationship types are used | null |

## Returns

| Name | Type | Description |
|-------|------|----------------------------------------------|
| nodes | List | List of visited nodes in breadth-first order |
| edges | List | List of edges traversed during the BFS |

## Examples

### Basic BFS Traversal

This example demonstrates a basic BFS traversal starting from a person node.


### Social Network Friend Recommendations

This example demonstrates how to use BFS to find potential friend recommendations in a social network.

#### Setup the Graph

```cypher
CREATE
(alice:Person {name: 'Alice', age: 28, city: 'New York'}),
(bob:Person {name: 'Bob', age: 32, city: 'Boston'}),
(charlie:Person {name: 'Charlie', age: 35, city: 'Chicago'}),
(david:Person {name: 'David', age: 29, city: 'Denver'}),
(eve:Person {name: 'Eve', age: 31, city: 'San Francisco'}),
(frank:Person {name: 'Frank', age: 27, city: 'Miami'}),

(alice)-[:FRIEND]->(bob),
(alice)-[:FRIEND]->(charlie),
(bob)-[:FRIEND]->(david),
(charlie)-[:FRIEND]->(eve),
(david)-[:FRIEND]->(frank),
(eve)-[:FRIEND]->(frank)
```

![Graph BFS](../images/graph_bfs.png)

#### Find Friends of Friends (Potential Recommendations)

```
// Find Alice's friends-of-friends (potential recommendations)
MATCH (alice:Person {name: 'Alice'})
CALL algo.bfs(alice, 2, 'FRIEND')
YIELD nodes

// Process results to get only depth 2 connections (friends of friends)
WHERE size(nodes) >= 3
WITH alice, nodes[2] AS potential_friend
WHERE NOT (alice)-[:FRIEND]->(potential_friend)
RETURN potential_friend
```

In this social network example, the BFS algorithm helps find potential friend recommendations by identifying people who are connected to Alice's existing friends but not directly connected to Alice yet.


## Performance Considerations

- **Indexing:** Ensure properties used for finding your starting node are indexed for optimal performance
- **Maximum Depth:** Choose an appropriate max_depth value based on your graph's connectivity; large depths in highly connected graphs can result in exponential growth of traversed nodes
- **Relationship Filtering:** When applicable, specify the relationship type to limit the traversal scope
- **Memory Management:** Be aware that the procedure stores visited nodes in memory to avoid cycles, which may require significant resources in large, densely connected graphs

## Error Handling

Common errors that may occur:

- **Null Starting Node:** If the start_node parameter is null, the procedure will raise an error; ensure your MATCH clause successfully finds the starting node
- **Invalid Relationship Type:** If you specify a relationship type that doesn't exist in your graph, the traversal will only include the starting node
- **Memory Limitations:** For large graphs with high connectivity, an out-of-memory error may occur if too many nodes are visited
- **Result Size:** If the BFS traversal returns too many nodes, query execution may be slow or time out; in such cases, try reducing the max_depth or filtering by relationship types
37 changes: 37 additions & 0 deletions algorithms/index.md
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# FalkorDB Algorithms Overview

FalkorDB offers a suite of graph algorithms optimized for high-performance graph analytics.
These algorithms are accessible via the `CALL algo.<name>()` interface and are built for speed and scalability using matrix-based computation.

This overview summarizes the available algorithms and links to their individual documentation.

## Table of Contents

- [Pathfinding Algorithms](#pathfinding-algorithms)
- [Centrality Measures](#centrality-measures)
- [Community Detection](#community-detection)

---

## Pathfinding Algorithms

- **[BFS](./bfs.md)**
Performs a breadth-first search starting from a source node and optionally stopping at target nodes or maximum depth.

- **[SPpath](./sppath.md)**
Computes the shortest paths between a source and one or more destination nodes.

- **[SSpath](./sspath.md)**
Enumerates all paths from a single source node to other nodes, based on constraints like edge filters and depth.

Comment on lines +28 to +33
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🛠️ Refactor suggestion

Align algorithm link text with procedure names
The display names SPpath and SSpath should match the actual procedures algo.SPpaths() and algo.SSpaths(). Update them as follows:

- - **[SPpath](./sppath.md)**
+ - **[SPpaths](./sppath.md)**
- - **[SSpath](./sspath.md)**
+ - **[SSpaths](./sspath.md)**
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
- **[SPpath](./sppath.md)**
Computes the shortest paths between a source and one or more destination nodes.
- **[SSpath](./sspath.md)**
Enumerates all paths from a single source node to other nodes, based on constraints like edge filters and depth.
- **[SPpaths](./sppath.md)**
Computes the shortest paths between a source and one or more destination nodes.
- **[SSpaths](./sspath.md)**
Enumerates all paths from a single source node to other nodes, based on constraints like edge filters and depth.
🤖 Prompt for AI Agents
In algorithms/index.md around lines 28 to 33, the displayed algorithm names
SPpath and SSpath do not match the actual procedure names algo.SPpaths() and
algo.SSpaths(). Update the link text to exactly match the procedure names by
changing SPpath to SPpaths and SSpath to SSpaths to ensure consistency and
clarity.

For path expressions like `shortestPath()` used directly in Cypher queries, refer to the [Cypher Path Functions section](../cypher/functions.md#path-functions).
## Centrality Measures

- **[PageRank](./pagerank.md)**
Computes the PageRank score of each node in the graph, representing its influence based on the structure of incoming links.

## Community Detection

- **[WCC (Weakly Connected Components)](./wcc.md)**
Finds weakly connected components in a graph, where each node is reachable from others ignoring edge directions.

97 changes: 97 additions & 0 deletions algorithms/pagerank.md
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---
title: "PageRank"
description: "PageRank"
---

# PageRank

## Introduction

PageRank is an algorithm that measures the importance of each node within the graph based on the number of incoming relationships and the importance of the corresponding source nodes.
The algorithm was originally developed by Google's founders Larry Page and Sergey Brin during their time at Stanford University.

## Algorithm Overview

PageRank works by counting the number and quality of relationships to a node to determine a rough estimate of how important that node is.
The underlying assumption is that more important nodes are likely to receive more connections from other nodes.

The algorithm assigns each node a score, where higher scores indicate greater importance.
The score for a node is derived recursively from the scores of the nodes that link to it, with a damping factor typically applied to prevent rank sinks.

## Syntax

The PageRank procedure has the following call signature:

```cypher
CALL pagerank.stream(
[label],
[relationship]
)
YIELD node, score
```

### Parameters

| Name | Type | Default | Description |
|----------------|--------|---------|------------------------------------------------------------------------------|
| `label` | String | null | The label of nodes to run the algorithm on. If null, all nodes are used. |
| `relationship` | String | null | The relationship type to traverse. If null, all relationship types are used. |

### Yield

| Name | Type | Description |
|---------|-------|--------------------------------------|
| `node` | Node | The node processed by the algorithm. |
| `score` | Float | The PageRank score for the node. |

## Examples

### Unweighted PageRank

First, let's create a sample graph representing a citation network between scientific papers:

```cypher
CREATE
(paper1:Paper {title: 'Graph Algorithms in Database Systems'}),
(paper2:Paper {title: 'PageRank Applications'}),
(paper3:Paper {title: 'Data Mining Techniques'}),
(paper4:Paper {title: 'Network Analysis Methods'}),
(paper5:Paper {title: 'Social Network Graph Theory'}),

(paper2)-[:CITES]->(paper1),
(paper3)-[:CITES]->(paper1),
(paper3)-[:CITES]->(paper2),
(paper4)-[:CITES]->(paper1),
(paper4)-[:CITES]->(paper3),
(paper5)-[:CITES]->(paper2),
(paper5)-[:CITES]->(paper4)
```

![Graph PR](../images/graph_page_rank.png)

Now we can run the PageRank algorithm on this citation network:

```cypher
CALL pagerank.stream('Paper', 'CITES')
YIELD node, score
RETURN node.title AS paper, score
ORDER BY score DESC
```

Expected results:

| paper | score |
|--------------------------------------|-------|
| Graph Algorithms in Database Systems | 0.43 |
| Data Mining Techniques | 0.21 |
| PageRank Applications | 0.19 |
| Network Analysis Methods | 0.14 |
| Social Network Graph Theory | 0.03 |


## Usage Notes

**Interpreting scores**:
- PageRank scores are relative, not absolute measures
- The sum of all scores in a graph equals 1.0
- Scores typically follow a power-law distribution
100 changes: 100 additions & 0 deletions algorithms/sppath.md
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---
title: "algo.SPpaths"
description: "Find shortest paths between two nodes with advanced cost and length constraints."
---

# `algo.SPpaths` - Shortest Path (Single Pair)

The `algo.SPpaths` procedure finds the shortest paths between a **source** and a **target** node, optionally constrained by cost, path length, and the number of paths to return.

It is designed for efficient and scalable computation of paths in large graphs, using properties like distance, time, or price as weights.

## Syntax

```cypher
CALL algo.SPpaths({
sourceNode: <node>,
targetNode: <node>,
relTypes: [<relationship_type>],
weightProp: <property>,
costProp: <property>, // optional
maxCost: <int>, // optional
maxLen: <int>, // optional
relDirection: "outgoing", // or "incoming", "both"
pathCount: <int> // 0 = all, 1 = single (default), n > 1 = up to n
})
YIELD path, pathWeight, pathCost
```

## Parameters

| Name | Type | Description |
|-----------------|----------|-------------|
| `sourceNode` | Node | Starting node |
| `targetNode` | Node | Destination node |
| `relTypes` | Array | List of relationship types to follow |
| `weightProp` | String | Property to minimize along the path (e.g., `dist`, `time`) |
| `costProp` | String | Property to constrain the total value (optional) |
| `maxCost` | Integer | Upper bound on total cost (optional) |
| `maxLen` | Integer | Max number of relationships in the path (optional) |
| `relDirection` | String | Traversal direction (`outgoing`, `incoming`, `both`) |
| `pathCount` | Integer | Number of paths to return (0 = all shortest, 1 = default, n = max number of results) |

## Returns

| Name | Type | Description |
|--------------|---------|-------------|
| `path` | Path | Discovered path from source to target |
| `pathWeight` | Integer | Sum of the weightProp across the path |
| `pathCost` | Integer | Sum of the costProp across the path (if used) |


## Examples:
Lets take this Road Network Graph as an example:

![Road network](../images/road_network.png)

### Example: Shortest Path by Distance from City A to City G:

```cypher
MATCH (a:City{name:'A'}), (g:City{name:'G'})
CALL algo.SPpaths({
sourceNode: a,
targetNode: g,
relTypes: ['Road'],
weightProp: 'dist'
})
YIELD path, pathWeight
RETURN pathWeight, [n in nodes(path) | n.name] AS pathNodes
```

#### Expected Result:
| pathWeight | pathNodes |
|------------|---------------|
| `12` | [A, D, E G] |


### Example: Bounded Cost Path from City A to City G:

```cypher
MATCH (a:City{name:'A'}), (g:City{name:'G'})
CALL algo.SPpaths({
sourceNode: a,
targetNode: g,
relTypes: ['Road'],
weightProp: 'dist',
costProp: 'time',
maxCost: 12,
pathCount: 2
})
YIELD path, pathWeight, pathCost
RETURN pathWeight, pathCost, [n in nodes(path) | n.name] AS pathNodes
```

#### Expected Result:
| pathWeight | pathCost | pathNodes |
|------------|----------| --------------- |
| `16` | `10` | [A, D, F G] |
| `14` | `12` | [A, D, C F, G] |

---
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