#17662: Evenly distributed sets
-------------------------------------+-------------------------------------
Reporter: vdelecroix | Owner:
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-6.5
Component: combinatorial | Resolution:
designs | Merged in:
Keywords: | Reviewers: Nathann Cohen
Authors: Vincent Delecroix | Work issues:
Report Upstream: N/A | Commit:
Branch: public/17662 | ac142f40af9a5df101cf7e312590d65bb71a307a
Dependencies: | Stopgaps:
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Changes (by ncohen):
* status: needs_review => needs_info
Comment:
Hellooooooooooooooooooo,
- Isn't it weird that all EDS not considered 'up to isomorphism' always
begin
with `0,1`? Perhaps you should say somewhere that they are always
normalized?
{{{
sage: E = EvenlyDistributedSetsBacktracker(Zmod(13), 4,
up_to_isomorphism=False)
sage: for B in E: print B
[0, 1, 11, 5]
[0, 1, 4, 6]
[0, 1, 9, 3]
[0, 1, 8, 10]
}}}
- `to_difference_family` -- could you add a check that this is indeed a
difference family? Like with the usual `check` argument?
- Same with `an_element`.
- "The value of the other" -- the value of the other what?
{{{
# Given one such function, the values of the other are 1/z, 1-z,
# 1/(1-z), (z-1)/z and z/(z-1).
}}}
- Why would that map `B[i]` to 1?
{{{
# We choose
# t -> (x - t)/ (x - B[j])
# (that maps x to 0 and B[i] to 1
}}}
- I do not get this line
{{{
# try to append x
if self._add_element(x,kk):
# note: the element x is already added to B in ._add_element()
if kk == k-1:
ans = self._B_automorphisms()
if ans is False:
continue
}}}
Wouldn't it be better to call `_B_automorphisms()` in
`self._add_element`, and
to not add the element if the min property is not satisfied?
- I do not understand why you do the same test twice:
{{{
if x == q-2:
kk -= 1
x = B[kk]
self._pop(kk)
if x == q-2:
kk -= 1
x = B[kk]
self._pop(kk)
if x == q-2:
}}}
Isn't it better to define x as "the last element in the list+1"? This
way you
couldn't have `x==q-2` when `B[kk-1]=q-2`
I added a small commit containing mostly doc. I also changed a bit the
management of `self.t`. I began by replacing your `if self.t[i]:
self.coset[i]=1` by a `self.coset[i] |= self.t[i]`, then noticed that it
was
probably why you had been setting t to zero outside of the `_add_element`
function.
It actually took me some time to understand that `t` was always equal to 0
when
this function was called. Because you initialized it elsewhere, I thought
for a
while that it used some values computed in another function.
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/17662#comment:24>
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