pd-code-rotate

Rotate the local representation of every crossing while respecting component orientation.

Installation

pip install pd-code-rotate

Usage example

from pd_code_rotate import rotate

pd = [[1, 5, 2, 4], [3, 1, 4, 6], [5, 3, 6, 2]]
print(rotate(pd))

Algorithm

Predecessor/successor maps determine the direction of each strand. For crossing [a,b,c,d], the implementation selects either [b,a,d,c] or [d,c,b,a] so the rotated crossing remains consistent with the canonical component direction. Arc incidences and crossing count are preserved.

Input conventions

A PD code is represented as a list of four-entry crossings. Arc labels normally occur exactly twice. Public functions validate inputs and return new values rather than mutating caller-owned data unless their API explicitly says otherwise.

External software

No external software is required.

Development

Run examples and package checks before release. Python packages require Python 3.10 or newer. Build PyPI artifacts with:

poetry check
poetry build

License

MIT. See LICENSE.