Implement (sub)direct sums of polytopes

[jplab]

From ​https://www.csun.edu/~ctoth/Handbook/chap15.pdf:

The (d+d)-dimensional polytope P⊕Q:=conv({(p,0)∈R^(d+d')|p∈P}∪{(0,p')∈R^(d+d')|q∈Q}). Thus the subdirect sum P⊕Q is a projection of the join P∗Q. The join is implemented in #24848.

Depends on #24848
Depends on #22572

CC: @videlec @mo271 @mkoeppe @fchapoton

Component: geometry

Keywords: days93, polytope

Author: Jean-Philippe Labbé

Branch/Commit: ffe21e2

Reviewer: Frédéric Chapoton

Issue created by migration from https://trac.sagemath.org/ticket/24849

[jplab]

Branch: u/jipilab/24849

[jplab]

New commits:

6eb0825

first version of (sub)direct sum

[jplab]

Dependencies: #24848, #22572

[jplab]

Commit: 6eb0825

[jplab]

Description changed:

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+++ 
@@ -1,3 +1,3 @@
 From ​https://www.csun.edu/~ctoth/Handbook/chap15.pdf:
 
-The (d+d)-dimensional polytope P⊕Q:=conv({(p,0)∈R<sup>(d+d')</sup>|p∈P}∪{(0,p')∈R<sup>(d+d')</sup>|q∈Q}). Thus the subdirect sum P⊕Q is a projection of the join P∗Q. (see #24848)
+The (d+d)-dimensional polytope P⊕Q:=conv({(p,0)∈R<sup>(d+d')</sup>|p∈P}∪{(0,p')∈R<sup>(d+d')</sup>|q∈Q}). Thus the subdirect sum P⊕Q is a projection of the join P∗Q. The join is implemented in #24848.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

b063975

typo

[sagetrac-git]

Changed commit from 6eb0825 to b063975

[sagetrac-git]

Changed commit from b063975 to d0242f3

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

d0242f3

removed translation from direct sum

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

0295def

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