Module graph 

Graph — pure-Rust port of igraph_t.

Storage is the indexed edge list that upstream igraph uses (see references/igraph/include/igraph_datatype.h:105-116):

• from[e], to[e] — canonical edge list. Edge e runs from from[e] to to[e]; |from| == |to| == ecount.
• oi[i] — edge ids ordered by from (and then to).
• ii[i] — edge ids ordered by to (and then from).
• os[v]..os[v+1] — slice of oi covering vertex v’s out-edges.
• is[v]..is[v+1] — slice of ii covering vertex v’s in-edges.

For undirected graphs the edge list is canonicalised so from[e] <= to[e] (matching upstream igraph’s invariant in type_indexededgelist.c:282-288). The doubled in/out indexing makes neighbors() symmetric for undirected graphs without storing each edge twice.

ALGO-CORE-001a (Phase 1, this file): struct + new/with_vertices + add_vertices/add_edge/add_edges + vcount/ecount/is_directed + neighbors/degree + Clone.

Follow-up AWUs:

• 001b: incident, edge-id helpers.
• 001c: delete_vertices/delete_edges.
• 001d: edge/edges/get_eid/get_eids/get_all_eids_between.
• 001e: property cache, is_same_graph.

Attribute system → ALGO-AT-* (out of scope here).

Structs

Graph

Counterpart of igraph_t (see references/igraph/include/igraph_datatype.h).

Type Aliases

EdgeId

Edge id. Same width as VertexId; an edge id is its position in from/to.

VertexId

Vertex id. The Phase-0 ADR-0007 fixes this to u32; Option<VertexId> is the idiomatic “no vertex” sentinel (igraph C uses -1).