passagemath-rankwidth

10.8.4 verified Fri May 01 auth: no python

passagemath-rankwidth provides functions for computing rankwidth and rank decompositions of graphs using the rw library. Part of the passagemath ecosystem. Current version: 10.8.4, released as part of passagemath 10.8. Release cadence follows passagemath releases (roughly 2-3 per year).

pip install passagemath-rankwidth

Common errors

error ModuleNotFoundError: No module named 'passagemath.graphs.rankwidth' ↓

cause The package passagemath-rankwidth is not installed or not properly imported.

fix

Run 'pip install passagemath-rankwidth' and ensure you use the correct import path: from passagemath.graphs.rankwidth import rankwidth

error ValueError: algorithm must be one of 'rw', 'cunningham', 'exact' ↓

cause You passed an invalid algorithm string.

fix

Use 'rw' or 'cunningham' (the latter replaces the deprecated 'exact').

error RuntimeError: rw executable not found ↓

cause The external 'rw' library is not installed on the system.

fix

Install rw (e.g., sudo apt install rw) or use algorithm='cunningham'.

Warnings

breaking The import path has changed from sage.graphs.rankwidth to passagemath.graphs.rankwidth. Old imports will fail. ↓

fix Use 'from passagemath.graphs.rankwidth import rankwidth' instead.

gotcha The rw algorithm (the default) uses the external 'rw' library, which must be installed as a system dependency. pip install does not install it automatically. ↓

fix Install the rw library (e.g., on Debian/Ubuntu: apt-get install rw) or set algorithm='cunningham' for a pure Python implementation.

deprecated The 'algorithm' parameter 'exact' is deprecated in favor of 'cunningham' for the exact decomposition method. ↓

fix Use algorithm='cunningham' instead of algorithm='exact'.

gotcha The function returns a tuple (rankwidth, decomposition). The decomposition is a linear ordering representation, not a tree. Do not expect a tree structure. ↓

fix Access the rankwidth as the first element, and the decomposition as the second.

Imports

rankwidth
wrong
```
from sage.graphs.rankwidth import rankwidth
```
correct
```
from passagemath.graphs.rankwidth import rankwidth
```
The old sage namespace is not available in passagemath; use passagemath prefix.

Quickstart

Compute the rankwidth of the Petersen graph using the rw algorithm.

from passagemath.graphs.rankwidth import rankwidth
g = graphs.PetersenGraph()
rw, decomp = rankwidth(g, algorithm='rw')
print(rw)