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28237 Implement Atkinson's algorithm for counting linear extensions of (tree) posets jmatherne jmatherne "We add two methods to posets.py:
- ""spectrum"" - This method has input a poset `P` and an element `a` of `P`. It outputs the `a`-spectrum of `P`, which is a list of integers whose i-th entry contains the number of linear extensions of `P` with `a` in the i-th position. In particular, the sum of the entries of the `a`-spectrum is the number of linear extensions of `P`.
- ""atkinson"" - This method has input a poset `P`, whose underlying undirected graph is a forest, and an element `a` of `P`. It uses Atkinson's algorithm (see reference below) to compute the `a`-spectrum of `P` (see definition of `a`-spectrum above).
M. D. Atkinson, ''On computing the number of linear extensions of a tree'', Order '''7''' (1990), 23-25." enhancement closed major sage-9.2 combinatorics fixed IMA Coding Sprints, days99, linear extensions, posets, trees, spectrum, gsoc2020 Galen Dorpalen-Barry, Bryan Gillespie, Jacob P. Matherne, Thomas McConville, Franco Saliola, Stefan Grosser Kevin Dilks, Bryan Gillespie, Travis Scrimshaw N/A bdf4b35a8e1acc544eb1c746c23a232603105afd