Multigraph

https://hexdocs.pm/multigraph/
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Multigraph is an Elixir library that provides a graph data structure supporting directed,...
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### Example for peek/1

Source: https://hexdocs.pm/multigraph/Multigraph.PriorityQueue.html

Shows creating a queue, pushing :foo with priority 1, peeking to get {:value, :foo}, popping to get the value, and confirming the popped value is :foo.

```elixir
iex> pq = Multigraph.PriorityQueue.new |> Multigraph.PriorityQueue.push(:foo, 1)
...> {:value, :foo} = Multigraph.PriorityQueue.peek(pq)
...> {{:value, val}, _} = Multigraph.PriorityQueue.pop(pq)
...> val
:foo
```

--------------------------------

### a_star/4 examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Examples showing successful path finding and a case where no path exists.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:b, :c}, {:c, :d}, {:b, :d}])
...> Multigraph.a_star(g, :a, :d, fn _ -> 0 end)
[:a, :b, :d]

iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = Multigraph.add_edges(g, [{:a, :c}, {:b, :c}, {:b, :d}])
...> Multigraph.a_star(g, :a, :d, fn _ -> 0 end)
nil
```

--------------------------------

### new/1 examples with options

Source: https://hexdocs.pm/multigraph/Multigraph.html

Shows examples of creating graphs with the new/1 function and its options. The examples demonstrate default directed graph, undirected type, custom vertex_identifier, and multigraph with partition_by. The output shows the resulting edges for each configuration.

```elixir
iex> Multigraph.new()
#Multigraph<type: directed, vertices: [], edges: []>

iex> g = Multigraph.new(type: :undirected) |> Multigraph.add_edges([{:a, :b}, {:b, :a}])
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b}]

iex> g = Multigraph.new(type: :directed) |> Multigraph.add_edges([{:a, :b}, {:b, :a}])
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b}, %Multigraph.Edge{v1: :b, v2: :a}]

iex> g = Multigraph.new(vertex_identifier: fn v -> :erlang.phash2(v) end) |> Multigraph.add_edges([{:a, :b}, {:b, :a}])
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b}, %Multigraph.Edge{v1: :b, v2: :a}]

iex> g = Multigraph.new(multigraph: true, partition_by: fn edge -> [edge.weight] end) |> Multigraph.add_edges([{:a, :b, weight: 1}, {:b, :a, weight: 2}])
...> Multigraph.edges(g, by: 1)
[%Multigraph.Edge{v1: :a, v2: :b, weight: 1}]
```

--------------------------------

### edges/2 examples with vertex and options

Source: https://hexdocs.pm/multigraph/Multigraph.html

Examples of using edges/2 to filter edges by vertex, by partition, or by a custom where function. The examples show results for existing and non-existing vertices, and for multigraph options.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> Multigraph.edges(g, :b) |> Enum.sort_by(& {&1.v1, &1.v2, &1.label})
[%Multigraph.Edge{v1: :a, v2: :b}, %Multigraph.Edge{v1: :b, v2: :c}]

iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> Multigraph.edges(g, :d)
[]

iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> g = Multigraph.add_edge(g, :a, :b, label: :contains)
...> Multigraph.edges(g, :a, by: [:contains])
[%Multigraph.Edge{v1: :a, v2: :b, label: :contains}]

iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> g = Multigraph.add_edge(g, :a, :b, label: :contains, weight: 2)
...> Multigraph.edges(g, :a, where: fn edge -> edge.weight == 2 end)
[%Multigraph.Edge{v1: :a, v2: :b, label: :contains, weight: 2}]
```

--------------------------------

### add_edge/2 example with Edge struct

Source: https://hexdocs.pm/multigraph/Multigraph.html

IEx example creating a graph and adding an edge using Multigraph.Edge.new/2.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edge(Multigraph.Edge.new(:a, :b))
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b}]
```

--------------------------------

### a_star/5 example with partition filtering

Source: https://hexdocs.pm/multigraph/Multigraph.html

IEx example showing A* search restricted to edges with label :fast using the :by option.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([
...>   {:a, :b, label: :fast, weight: 1},
...>   {:a, :c, label: :slow, weight: 10},
...>   {:b, :d, label: :fast, weight: 1},
...>   {:c, :d, label: :slow, weight: 1}
...> ])
...> Multigraph.a_star(g, :a, :d, fn _ -> 0 end, by: :fast)
[:a, :b, :d]
```

--------------------------------

### add_edge/4 examples with default and custom options

Source: https://hexdocs.pm/multigraph/Multigraph.html

Two IEx examples showing edge creation with default options and with label and weight options.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edge(:a, :b)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b, label: nil, weight: 1}]
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_edge(:a, :b, label: :foo, weight: 2)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo, weight: 2}]
```

--------------------------------

### edges/3 default example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of edges/3 with default options, returning all edges between :a and :b sorted by label.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edge(:a, :b, label: :uses)
...> g = Multigraph.add_edge(g, :a, :b, label: :contains)
...> Multigraph.edges(g, :a, :b) |> Enum.sort_by(& &1.label)
[%Multigraph.Edge{v1: :a, v2: :b, label: :contains}, %Multigraph.Edge{v1: :a, v2: :b, label: :uses}]
```

--------------------------------

### postorder/1 example with graph diagram

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of postorder/1. The first block shows the graph structure, the second builds it and returns the postorder traversal result.

```text
    :a
                 :b
      /           :c   :d
    /
   :e
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d, :e])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:b, :c}, {:b, :d}, {:c, :e}])
...> Multigraph.postorder(g)
[:e, :c, :d, :b, :a]
```

--------------------------------

### preorder/1 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of using Multigraph.preorder/1 on a graph with vertices :a, :b, :c, :d, :e and edges :a-:b, :b-:c, :b-:d, :c-:e. The result is [:a, :b, :c, :e, :d].

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d, :e])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:b, :c}, {:b, :d}, {:c, :e}])
...> Multigraph.preorder(g)
[:a, :b, :c, :e, :d]
```

--------------------------------

### info/1 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example for info/1. Creates a directed graph with four vertices and two edges, then checks that info/1 returns a map with type :directed, num_vertices 4, and num_edges 2. The match returns true.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = g |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> match?(%{type: :directed, num_vertices: 4, num_edges: 2}, Multigraph.info(g))
true
```

--------------------------------

### num_vertices/1 spec and example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the num_vertices/1 function and shows an example that adds three vertices and returns the vertex count.

```elixir
@spec num_vertices(t()) :: non_neg_integer()
```

```elixir
iex> g = Multigraph.add_vertices(Multigraph.new, [:a, :b, :c])
...> Multigraph.num_vertices(g)
3
```

--------------------------------

### components/1 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of components/1. The graph has vertices :a, :b, :c, and :d, and the function returns a single connected component containing all vertices.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}, {:b, :c}, {:c, :d}, {:c, :a}])
...> Multigraph.components(g)
[[:d, :b, :c, :a]]
```

--------------------------------

### neighbors/2 spec and examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the neighbors/2 function signature and shows examples. It returns all neighboring vertices of the given vertex. The examples show returning neighbors for an existing vertex and an empty list for a non-existent vertex.

```elixir
@spec neighbors(t(), vertex()) :: [vertex()]
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:b, :a}, {:b, :c}, {:c, :a}])
...> Multigraph.neighbors(g, :a)
[:b, :c]

iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:b, :a}, {:b, :c}, {:c, :a}])
...> Multigraph.neighbors(g, :d)
[]
```

--------------------------------

### loop_vertices/1 spec and example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the loop_vertices/1 function signature and shows an example. It returns a list of vertices that are part of a loop (a cycle of length 1). The example creates a graph with a self-loop on :a and returns [:a].

```elixir
@spec loop_vertices(t()) :: [vertex()]
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c]) |> Multigraph.add_edge(:a, :a)
...> Multigraph.loop_vertices(g)
[:a]
```

--------------------------------

### edges/1 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of using edges/1 to list all edges in a graph. The output is sorted by vertex and label, showing edges from :a to :c and :b to :c.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertex(:a) |> Multigraph.add_vertex(:b) |> Multigraph.add_vertex(:c)
...> g = g |> Multigraph.add_edge(:a, :c) |> Multigraph.add_edge(:b, :c)
...> Multigraph.edges(g) |> Enum.sort_by(& {&1.v1, &1.v2, &1.label})
[%Multigraph.Edge{v1: :a, v2: :c}, %Multigraph.Edge{v1: :b, v2: :c}]
```

--------------------------------

### delete_edge/3 directed example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example for delete_edge/3 on a directed graph, showing that all edges between :a and :b are removed.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}])
...> g = Multigraph.delete_edge(g, :a, :b)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g) []
```

--------------------------------

### edges/3 undirected example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of edges/3 with an undirected graph, returning all edges between :a and :b sorted by label.

```elixir
iex> g = Multigraph.new(type: :undirected) |> Multigraph.add_edge(:a, :b, label: :uses)
...> g = Multigraph.add_edge(g, :a, :b, label: :contains)
...> Multigraph.edges(g, :a, :b) |> Enum.sort_by(& &1.label)
[%Multigraph.Edge{v1: :a, v2: :b, label: :contains}, %Multigraph.Edge{v1: :a, v2: :b, label: :uses}]
```

--------------------------------

### reachable/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of using Multigraph.reachable/2 on a graph with vertices :a, :b, :c, :d and edges :a-:b, :a-:c, :b-:c, :c-:d. The result is [:d, :c, :b, :a].

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}, {:b, :c}, {:c, :d}])
...> Multigraph.reachable(g, [:a])
[:d, :c, :b, :a]
```

--------------------------------

### bellman_ford/3 with :by option example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of bellman_ford/3 with the :by option set to :fast. The result is the distance to vertex :c, which is 3, ignoring the slow edge.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([
...>   {:a, :b, label: :fast, weight: 1},
...>   {:b, :c, label: :fast, weight: 2},
...>   {:a, :c, label: :slow, weight: 100}
...> ])
...> distances = Multigraph.bellman_ford(g, :a, by: :fast)
...> distances[:c]
3
```

--------------------------------

### Construct a k-core with k_core_components/1

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of constructing a k-core for a given graph using k_core_components/1. Filters vertices by a desired k value and then builds a subgraph with Multigraph.subgraph/2.

```elixir
k_core_vertices =
  g
  |> Multigraph.k_core_components()
  |> Stream.filter(fn {k, _} -> k >= desired_k end)
  |> Enum.flat_map(fn {_, vs} -> vs end)
Multigraph.subgraph(g, k_core_vertices)
```

--------------------------------

### BFS reduce example

Source: https://hexdocs.pm/multigraph/Multigraph.Reducers.Bfs.html

Performs a breadth-first traversal of the graph, applying the reducer function to each vertex and the accumulator. The algorithm follows lower-weighted edges first. The result is the final accumulator state. The example shows a basic reduction that prepends vertices to the accumulator.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 3}])
...> Elixir.Multigraph.Reducers.Bfs.reduce(g, [], fn v, acc -> {:next, [v|acc]} end)
[2, 4, 3, 1]
```

--------------------------------

### dijkstra/4 with :by option example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of using Multigraph.dijkstra/4 with the :by option to filter edges by partition key. The graph is created with multigraph: true and edges with labels and weights. The result is the shortest path [:a, :b, :d] when restricting traversal to edges with label :fast.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([
...>   {:a, :b, label: :fast, weight: 1},
...>   {:a, :c, label: :slow, weight: 10},
...>   {:b, :d, label: :fast, weight: 1},
...>   {:c, :d, label: :slow, weight: 1}
...> ])
...> Multigraph.dijkstra(g, :a, :d, by: :fast)
[:a, :b, :d]
```

--------------------------------

### Example for pop/1

Source: https://hexdocs.pm/multigraph/Multigraph.PriorityQueue.html

Shows popping elements in priority order from a shuffled queue, ending with :empty when the queue is exhausted.

```elixir
iex> pq = Multigraph.PriorityQueue.new
...> pq = Enum.reduce(Enum.shuffle(0..4), pq, fn i, pq -> Multigraph.PriorityQueue.push(pq, ?a+i, i) end)
...> {{:value, ?a}, pq} = Multigraph.PriorityQueue.pop(pq)
...> {{:value, ?b}, pq} = Multigraph.PriorityQueue.pop(pq)
...> {{:value, ?c}, pq} = Multigraph.PriorityQueue.pop(pq)
...> {{:value, ?d}, pq} = Multigraph.PriorityQueue.pop(pq)
...> {{:value, ?e}, pq} = Multigraph.PriorityQueue.pop(pq)
...> {result, _} = Multigraph.PriorityQueue.pop(pq)
...> result
:empty
```

--------------------------------

### Example for push/3

Source: https://hexdocs.pm/multigraph/Multigraph.PriorityQueue.html

Shows pushing elements with priorities and popping them, including two separate scenarios: one with a single element and one with two elements of the same priority.

```elixir
iex> pq = Multigraph.PriorityQueue.new
...> pq = Multigraph.PriorityQueue.push(pq, :foo, 1)
...> {result, _} = Multigraph.PriorityQueue.pop(pq)
...> result
{:value, :foo}

iex> pq = Multigraph.PriorityQueue.new
...> pq = Multigraph.PriorityQueue.push(pq, :foo, 1)
...> {{:value, :foo}, pq} = Multigraph.PriorityQueue.pop(pq)
...> pq = Multigraph.PriorityQueue.push(pq, :bar, 1)
...> {result, _} = Multigraph.PriorityQueue.pop(pq)
...> result
{:value, :bar}
```

--------------------------------

### delete_edge/3 undirected example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example for delete_edge/3 on an undirected graph, showing that all edges between :a and :b are removed.

```elixir
iex> g = Multigraph.new(type: :undirected) |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}])
...> g = Multigraph.delete_edge(g, :a, :b)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g) []
```

--------------------------------

### in_edges/3 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example for in_edges/3. Creates a multigraph with two labeled edges from :a to :b, then filters the in edges to :b by the partition :foo. The result contains only the edge with label :foo.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b, label: :foo}, {:a, :b, label: :bar}])
...> Multigraph.in_edges(g, :b, by: :foo)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo}]
```

--------------------------------

### label_vertex/3 spec and examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the label_vertex/3 function signature and shows usage examples. The function updates labels for a vertex; if the vertex does not exist, it returns {:error, {:invalid_vertex, v}}. The examples demonstrate adding a label and replacing labels with a list.

```elixir
@spec label_vertex(t(), vertex(), term()) ::
  t() | {:error, {:invalid_vertex, vertex()}}
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertex(:a, :foo)
...> [:foo] = Multigraph.vertex_labels(g, :a)
...> g = Multigraph.label_vertex(g, :a, :bar)
...> Multigraph.vertex_labels(g, :a)
[:foo, :bar]

iex> g = Multigraph.new |> Multigraph.add_vertex(:a)
...> g = Multigraph.label_vertex(g, :a, [:foo, :bar])
...> Multigraph.vertex_labels(g, :a)
[:foo, :bar]
```

--------------------------------

### out_neighbors/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of using out_neighbors/2. It returns the unique vertices reachable from :a, which is [:b] even though there are two edges to :b.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}, {:b, :c}])
...> Multigraph.out_neighbors(g, :a)
[:b]
```

--------------------------------

### Add edges from tuples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example showing add_edges/2 with tuples of {vertex, vertex} and {vertex, vertex, edge_opts} including label and weight options. The result is sorted by vertices and label.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}, {:a, :b, label: :foo, weight: 2}])
...> Multigraph.edges(g) |> Enum.sort_by(& {&1.v1, &1.v2, &1.label})
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo, weight: 2}, %Multigraph.Edge{v1: :a, v2: :b}]
```

--------------------------------

### in_neighbors/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example for in_neighbors/2. Creates a directed multigraph with edges from :a to :b (including a labeled edge) and from :b to :c, then returns the in neighbors of :b. The result is [:a].

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}, {:b, :c}])
...> Multigraph.in_neighbors(g, :b)
[:a]
```

--------------------------------

### out_degree/2 spec and example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the out_degree/2 function and shows an example that builds a graph with vertices and one edge, then returns the out-degree of vertex :a. For undirected graphs, in-degree and out-degree are always the same.

```elixir
@spec out_degree(t(), vertex()) :: non_neg_integer()
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c]) |> Multigraph.add_edge(:a, :b)
...> Multigraph.out_degree(g, :a)
1
```

--------------------------------

### edges/3 with :by option

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of edges/3 with multigraph: true and the :by option to filter edges by partition label.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> g = Multigraph.add_edge(g, :a, :b, label: :contains)
...> Multigraph.edges(g, :a, by: :contains)
[%Multigraph.Edge{v1: :a, v2: :b, label: :contains}]
```

--------------------------------

### edges/3 with :by and :where options

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of edges/3 with multigraph: true, the :by option, and a :where function filtering edges by weight.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b}, {:b, :c}])
...> g = Multigraph.add_edge(g, :a, :b, label: :contains, weight: 2)
...> Multigraph.edges(g, :a, by: :contains, where: fn edge -> edge.weight == 2 end)
[%Multigraph.Edge{v1: :a, v2: :b, label: :contains, weight: 2}]
```

--------------------------------

### reachable_neighbors/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of using Multigraph.reachable_neighbors/2 on a graph with vertices :a, :b, :c, :d and edges :a-:b, :a-:c, :b-:c, :c-:d. The result is [:d, :c, :b].

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}, {:b, :c}, {:c, :d}])
...> Multigraph.reachable_neighbors(g, [:a])
[:d, :c, :b]
```

--------------------------------

### out_edges/3 with :by and :where options

Source: https://hexdocs.pm/multigraph/Multigraph.html

Examples of using out_edges/3 with the :by and :where options. The first filters by partition key :foo, the second adds a predicate on edge weight. Both require multigraph: true.

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b, label: :foo}, {:a, :b, label: :bar}, {:a, :c}])
...> Multigraph.out_edges(g, :a, by: :foo)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo}]
```

```elixir
iex> g = Multigraph.new(multigraph: true) |> Multigraph.add_edges([{:a, :b, label: :foo, weight: 5}, {:a, :b, label: :bar}])
...> Multigraph.out_edges(g, :a, by: :foo, where: fn e -> e.weight > 1 end)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo, weight: 5}]
```

--------------------------------

### delete_edge/4 examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Examples for delete_edge/4: passing nil removes the unlabelled edge, passing :foo removes the labelled edge, and the undirected case removes the labelled edge.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}])
...> g = Multigraph.delete_edge(g, :a, :b, nil)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo}]

iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}])
...> g = Multigraph.delete_edge(g, :a, :b, :foo)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b, label: nil}]

iex> g = Multigraph.new(type: :undirected) |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}])
...> g = Multigraph.delete_edge(g, :a, :b, :foo)
...> [:a, :b] = Multigraph.vertices(g)
...> Multigraph.edges(g)
[%Multigraph.Edge{v1: :a, v2: :b, label: nil}]
```

--------------------------------

### edge/3 and edge/4 examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Examples of using Multigraph.edge/3 and edge/4. The first call with reversed vertices returns nil. The second returns an Edge struct without a label. The third returns an Edge with the specified label. The fourth shows that for an undirected graph, the edge is found regardless of vertex order.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :contains}, {:a, :b, label: :uses}])
...> Multigraph.edge(g, :b, :a)
nil

iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :contains}, {:a, :b, label: :uses}])
...> Multigraph.edge(g, :a, :b)
%Multigraph.Edge{v1: :a, v2: :b}

iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :contains}, {:a, :b, label: :uses}])
...> Multigraph.edge(g, :a, :b, :contains)
%Multigraph.Edge{v1: :a, v2: :b, label: :contains}

iex> g = Multigraph.new(type: :undirected) |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :contains}, {:a, :b, label: :uses}])
...> Multigraph.edge(g, :a, :b, :contains)
%Multigraph.Edge{v1: :a, v2: :b, label: :contains}
```

--------------------------------

### bellman_ford/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example of bellman_ford/2. The first graph returns a map of distances from vertex :a, while the second graph contains a negative cycle and returns nil.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([
...>   {:b, :c, weight: -2}, {:a, :b, weight: 1},
...>   {:c, :d, weight: 3}, {:b, :d, weight: 4}])
...> Multigraph.bellman_ford(g, :a)
%{a: 0, b: 1, c: -1, d: 2}

iex> g = Multigraph.new |> Multigraph.add_edges([
...>   {:b, :c, weight: -2}, {:a, :b, weight: -1},
...>   {:c, :d, weight: -3}, {:d, :a, weight: -5}])
...> Multigraph.bellman_ford(g, :a)
nil
```

--------------------------------

### add_vertex/3 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Shows adding a vertex with a single label and with a list of labels. The second add_vertex call is a no-op because the vertex already exists.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertex(:a, :mylabel) |> Multigraph.add_vertex(:a)
...> [:a] = Multigraph.vertices(g)
...> Multigraph.vertex_labels(g, :a)
[:mylabel]

iex> g = Multigraph.new |> Multigraph.add_vertex(:a, [:mylabel, :other])
...> Multigraph.vertex_labels(g, :a)
[:mylabel, :other]
```

--------------------------------

### get_paths/3 IEx example

Source: https://hexdocs.pm/multigraph/Multigraph.html

IEx session showing get_paths/3 usage. The first graph returns two paths between :a and :d; the second graph has no path and returns an empty list.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:b, :c}, {:c, :d}, {:b, :d}, {:c, :a}])
...> Multigraph.get_paths(g, :a, :d)
[[:a, :b, :c, :d], [:a, :b, :d]]

iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = Multigraph.add_edges(g, [{:a, :c}, {:b, :c}, {:b, :d}])
...> Multigraph.get_paths(g, :a, :d)
[]
```

--------------------------------

### num_edges/1 spec and example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the num_edges/1 function and shows an example that adds edges (including a self-loop) and returns the edge count. Pseudo-edges (label/weight pairs) are not counted; only distinct vertex pairs with an edge are counted.

```elixir
@spec num_edges(t()) :: non_neg_integer()
```

```elixir
iex> g = Multigraph.add_edges(Multigraph.new, [{:a, :b}, {:b, :c}, {:a, :a}])
...> Multigraph.num_edges(g)
3
```

--------------------------------

### reduce/3 examples: DFS traversal with reducer function

Source: https://hexdocs.pm/multigraph/Multigraph.Reducers.Dfs.html

Performs a depth-first traversal of the graph, applying the reducer function to each new vertex and the accumulator. The algorithm follows lower-weighted edges first. The result is the accumulator state after the last reduction. The examples show basic reduction, skipping a vertex, and halting early.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 4}])
...> Elixir.Multigraph.Reducers.Dfs.reduce(g, [], fn v, acc -> {:next, [v|acc]} end)
[4, 2, 3, 1]
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4, 5])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 4}, {4, 5}])
...> Elixir.Multigraph.Reducers.Dfs.reduce(g, [], fn 5, acc -> {:skip, acc}; v, acc -> {:next, [v|acc]} end)
[4, 2, 3, 1]
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4, 5])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 4}, {4, 5}])
...> Elixir.Multigraph.Reducers.Dfs.reduce(g, [], fn 4, acc -> {:halt, acc}; v, acc -> {:next, [v|acc]} end)
[2, 3, 1]
```

--------------------------------

### in_edges/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example for in_edges/2. Creates a directed multigraph with edges including a labeled edge, then returns the in edges to vertex :b sorted by label. The result includes both the labeled and unlabeled edges.

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}, {:b, :c}])
...> Multigraph.in_edges(g, :b) |> Enum.sort_by(& &1.label)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo}, %Multigraph.Edge{v1: :a, v2: :b}]
```

--------------------------------

### add_vertices/2 example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Adds a list of vertices, including a duplicate, and returns the unique vertices.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :a])
...> Multigraph.vertices(g)
[:a, :b]
```

--------------------------------

### out_edges/2 spec and example

Source: https://hexdocs.pm/multigraph/Multigraph.html

Specifies the out_edges/2 function and shows an example that adds edges (including one with a label) and returns the out edges from vertex :a, sorted by label. For undirected graphs, it delegates to edges/2.

```elixir
@spec out_edges(t(), vertex()) :: Multigraph.Edge.t()
```

```elixir
iex> g = Multigraph.new |> Multigraph.add_edges([{:a, :b}, {:a, :b, label: :foo}, {:b, :c}])
...> Multigraph.out_edges(g, :a) |> Enum.sort_by(& &1.label)
[%Multigraph.Edge{v1: :a, v2: :b, label: :foo}, %Multigraph.Edge{v1: :a, v2: :b}]
```

--------------------------------

### batch_topsort/1 examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

Shows batch topological sorting on various graphs, including a cyclic graph that returns false. Multiple edges are treated as a single edge.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}])
...> Multigraph.batch_topsort(g)
[[:a], [:b, :c]]

iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}, {:b, :c}, {:c, :d}])
...> Multigraph.batch_topsort(g)
[[:a], [:b], [:c], [:d]]

iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d, :x, :y, :z])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}, {:c, :d}, {:x, :y}, {:x, :z}])
...> Multigraph.batch_topsort(g)
[[:a, :x], [:b, :c, :y, :z], [:d]]

iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c, :d, :x, :y, :z])
...> g = Multigraph.add_edges(g, [{:a, :b}, {:a, :c}, {:b, :c}, {:c, :d}, {:c, :a}])
...> Multigraph.batch_topsort(g)
false
```

--------------------------------

### degree/2 IEx examples

Source: https://hexdocs.pm/multigraph/Multigraph.html

IEx examples for degree/2. Shows that for an undirected graph and a directed graph (default), the degree of vertex :b is 1 after adding a single edge.

```elixir
iex> g = Multigraph.new(type: :undirected) |> Multigraph.add_vertices([:a, :b, :c]) |> Multigraph.add_edge(:a, :b)
...> Multigraph.degree(g, :b)
1

iex> g = Multigraph.new() |> Multigraph.add_vertices([:a, :b, :c]) |> Multigraph.add_edge(:a, :b)
...> Multigraph.degree(g, :b)
1
```

--------------------------------

### Add edges from Edge structs

Source: https://hexdocs.pm/multigraph/Multigraph.html

Example showing add_edges/2 with a list of Edge structs created via Edge.new/2 and Edge.new/3, including a weight option. The result is sorted by vertices and label.

```elixir
iex> alias Multigraph.Edge
...> edges = [Edge.new(:a, :b), Edge.new(:b, :c, weight: 2)]
...> g = Multigraph.new |> Multigraph.add_vertices([:a, :b, :c]) |> Multigraph.add_edges(edges)
...> Multigraph.edges(g) |> Enum.sort_by(& {&1.v1, &1.v2, &1.label})
[%Multigraph.Edge{v1: :a, v2: :b}, %Multigraph.Edge{v1: :b, v2: :c, weight: 2}]
```

--------------------------------

### has_vertex?/2 IEx example

Source: https://hexdocs.pm/multigraph/Multigraph.html

IEx session showing has_vertex?/2 usage. Returns true for an existing vertex and false for a missing vertex.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b])
...> Multigraph.has_vertex?(g, :a)
true

iex> g = Multigraph.new |> Multigraph.add_vertices([:a, :b])
...> Multigraph.has_vertex?(g, :c)
false
```

--------------------------------

### BFS map example

Source: https://hexdocs.pm/multigraph/Multigraph.Reducers.Bfs.html

Performs a breadth-first traversal of the graph, applying the mapping function to each vertex. The algorithm follows lower-weighted edges first. Returns a list of values from the mapper in encounter order.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 3}])
...> Elixir.Multigraph.Reducers.Bfs.map(g, fn v -> v end)
[1, 3, 4, 2]
```

--------------------------------

### BFS reduce with skip example

Source: https://hexdocs.pm/multigraph/Multigraph.Reducers.Bfs.html

Performs a breadth-first traversal of the graph, applying the reducer function to each vertex and the accumulator. The algorithm follows lower-weighted edges first. The reducer can return {:skip, acc} to skip a vertex, as shown for vertex 5.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 3}, {4, 5}])
...> Elixir.Multigraph.Reducers.Bfs.reduce(g, [], fn 5, acc -> {:skip, acc}; v, acc -> {:next, [v|acc]} end)
[2, 4, 3, 1]
```

--------------------------------

### BFS reduce with halt example

Source: https://hexdocs.pm/multigraph/Multigraph.Reducers.Bfs.html

Performs a breadth-first traversal of the graph, applying the reducer function to each vertex and the accumulator. The algorithm follows lower-weighted edges first. The reducer can return {:halt, acc} to stop traversal early, as shown for vertex 4.

```elixir
iex> g = Multigraph.new |> Multigraph.add_vertices([1, 2, 3, 4])
...> g = Multigraph.add_edges(g, [{1, 3}, {1, 4}, {3, 2}, {2, 3}, {4, 5}])
...> Elixir.Multigraph.Reducers.Bfs.reduce(g, [], fn 4, acc -> {:halt, acc}; v, acc -> {:next, [v|acc]} end)
[3, 1]
```
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