#17053: Add function for direct sum of posets
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Reporter: jmantysalo | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-wishlist
Component: combinatorics | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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Sage has no function for direct sum of posets. What kind of function it
should be?
Let's say that poset `P` has elements `a` and `b`, `Q` has elements `c`
and `d`. Then sum on P and Q could have elements
1) a,b,c,d. Function would check that there are no common elements.
2) (1,a),(1,b),(2,c),(2,c). Optional parameter would change first element
of tuples.
3) 0,1,2,3. Function would just make poset isomorphic to P+Q with integer
elements.
Now, it would be nice to have also sum of arbitrary number of posets. So
function could be something like
`P.direct_sum(Q)` (case 1 as default?)
`P.direct_sum(Q, labeling='default')` (case 2 / default)
`P.direct_sum(Q, labeling=lambda n: chr(ord('a')+n))` (case 2 / non-
default)
`P.direct_sum(Q, labeling='plain')` (case 3)
and if possible, accept something like
`P1.direct_sum(P2, P3, P4, labeling=...)`
Does this sound reasonable?
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Ticket URL: <http://trac.sagemath.org/ticket/17053>
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