# pgRouting Manual (3.6)

## BFS - Category

- pgr_kruskalBFS

- pgr_primBFS

Traversal using breadth first search.

- It’s implementation is only on undirected graph.

- Process is done only on edges with positive costs.

- When the graph is connected

  - The resulting edges make up a tree

- When the graph is not connected,

  - Finds a minimum spanning tree for each connected component.

  - The resulting edges make up a forest.

## Parameters

Parameter | Type | Description
--- | --- | ---
Edges SQL | `TEXT` | Edges SQL as described below.

root vid

`BIGINT`

Identifier of the root vertex of the tree.

- When value is \(0\) then gets the spanning forest starting in aleatory nodes for each tree in the forest.

root vids

`ARRAY` [ ANY-INTEGER ]

Array of identifiers of the root vertices.

> - \(0\) values are ignored

> - For optimization purposes, any duplicated value is ignored.

Where:

ANY-INTEGER:

  SMALLINT, INTEGER, BIGINT

ANY-NUMERIC:

  SMALLINT, INTEGER, BIGINT, REAL, FLOAT, NUMERIC

### BFS optional parameters

Parameter | Type | Default | Description
--- | --- | --- | ---

`max_depth`

`BIGINT`

\(9223372036854775807\)

Upper limit of the depth of the tree.

- When negative throws an error.

## Inner Queries

### Edges SQL

Column | Type | Default | Description
--- | --- | --- | ---
`id` | ANY-INTEGER |  | Identifier of the edge.
`source` | ANY-INTEGER |  | Identifier of the first end point vertex of the edge.
`target` | ANY-INTEGER |  | Identifier of the second end point vertex of the edge.
`cost` | ANY-NUMERICAL |  | Weight of the edge (`source`, `target`)

`reverse_cost`

ANY-NUMERICAL

-1

Weight of the edge (`target`, `source`)

- When negative: edge (`target`, `source`) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER:

  `SMALLINT`, `INTEGER`, `BIGINT`

ANY-NUMERICAL:

  `SMALLINT`, `INTEGER`, `BIGINT`, `REAL`, `FLOAT`

## Result columns

Returns set of `(seq, depth, start_vid, node, edge, cost, agg_cost)`

Parameter | Type | Description
--- | --- | ---
`seq` | `BIGINT` | Sequential value starting from \(1\).

`depth`

`BIGINT`

Depth of the `node`.

- \(0\) when `node` = `start_vid`.

`start_vid` | `BIGINT` | Identifier of the root vertex.
`node` | `BIGINT` | Identifier of `node` reached using `edge`.

`edge`

`BIGINT`

Identifier of the `edge` used to arrive to `node`.

- \(-1\) when `node` = `start_vid`.

`cost` | `FLOAT` | Cost to traverse `edge`.
`agg_cost` | `FLOAT` | Aggregate cost from `start_vid` to `node`.

Where:

ANY-INTEGER:

  SMALLINT, INTEGER, BIGINT

ANY-NUMERIC:

  SMALLINT, INTEGER, BIGINT, REAL, FLOAT, NUMERIC

## See Also

- Boost: Prim’s algorithm

- Boost: Kruskal’s algorithm

- Wikipedia: Prim’s algorithm

- Wikipedia: Kruskal’s algorithm

Indices and tables

- Index

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