Topology

Topology parsing and graph construction is implemented in src/topos/build.rs.

Days supports three input modes:

1. Fat-tree ([topology] category = "FatTree")
2. Torus ([topology] category = "Torus")
3. Custom graph (omit [topology], provide edges and hosts)

All modes ultimately produce:

• an undirected graph UnGraph<usize, ()> (nodes are usize IDs),
• a hosts: Vec<usize> list indicating which nodes can host flow endpoints.

1) Custom topology (explicit edges)

Use this mode when you want exact control over the graph:

edges = [[0, 1], [0, 2]]
hosts = [0, 1, 2]

• edges is a list of undirected edges (pairs of node IDs).
• hosts is a list of node IDs that can host sources/sinks.

2) Fat-tree

[topology]
category = "FatTree"

[topology.fat_tree]
k = 8

Constraints:

• k must be even and positive.

Notes:

• Days constructs the canonical k-ary fat-tree and sets hosts = 0..(k^2/2).

3) Torus

[topology]
category = "Torus"

[topology.torus]
dim = 2
n = 3

Constraints:

• dim must be 1, 2, or 3.
• n must be positive.

Notes:

• Days builds a wrap-around torus and sets hosts = 0..(n^dim).

Common failure modes

• Missing the required sub-table ([topology.fat_tree] or [topology.torus]) for the chosen category.
• Using fewer than 2 hosts when you rely on random endpoint selection (flow sets, collective endpoint generation).