#19418: skew-Hadamard matrices and related srg's
-------------------------+-------------------------------------------------
Reporter: | Owner:
dimpase | Status: needs_work
Type: | Milestone: sage-6.10
enhancement | Resolution:
Priority: major | Merged in:
Component: | Reviewers: Nathann Cohen
combinatorics | Work issues:
Keywords: | Commit:
Authors: | c5a7eee39d4c6dce006d1f6f8fd7a23383d540b7
Report Upstream: N/A | Stopgaps:
Branch: |
public/19418 |
Dependencies: |
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Changes (by ncohen):
* status: needs_review => needs_work
* reviewer: => Nathann Cohen
Comment:
Helloooooo Dima,
First-pass review:
- Why don't you call `normalise_hadamard` instead of adding a keyword
inside of
`hadamard_matrix_paleyI` (without changing `hadamard_matrix_paleyII`)?
Those
two functions are not directly available to the users, who are meant to
call
`hadamard_matrix` directly.
- `is_hadamard_martrix` -- could you move 'skew=False' to before
'verbose=False'
? Usually the verbosity/check flags are the last ones to appear as they
do not
change the behaviour of the functon.
- Call `is_skew_symmetric` instead of doing it yourself. In theory you
shouldn't
have to create two copies of the matrix in memory in order to check
that.
- `zero_position=1` -- you have to write documentation for private
functions
too. Does [the paraeter that you add] appear in the lemma cited in the
docstring?
- `zero_position=1` -- if you meant `True`, write `True`.
- `_circulant_matrix` -- if it does not exist yet, this constructor should
be
added in the matrix/ code and be available through `matrix.<tab>`
- `mod(j-i,n)` is `(j-i)%n`. One day you will have to accept that you
write
Python code.
- Instead of a `_GS_skew_hadamard` function that encodes 4 matrices, why
don't
you reserve cases `if n == 36' (and others) in the main function
`skew_hadamard_matrix`? That would also solve the problem that this
function
has no documentation whatsoever.
- 'and' (see wikipedia:
https://en.wikipedia.org/wiki/Bitwise_operation#AND) is
a useful operator in computer science. E.g.:
{{{
+ if M is None: # try Williamson-Goethals-Seidel construction
+ if _GS_skew_hadamard(n, existence=True):
}}}
becomes
{{{
+ if M is None and_GS_skew_hadamard(n, existence=True):
}}}
- `switch_skewhad_pow2` -- please respect the current standard for the
names in
`graphs.<tab>`. Upper case, no underscore, ends with `Graph`. Actually,
it
could be named 'SwitchSkewhadGraph` and only mention the `pow2` part in
the
docstring.
- `graphs.Pseudo_L_2n_4n_m_1`? Seriously? If you cannot give it a clear
and
meaningful name easily, then take it as a sign that this function should
not
be exposed to the users directly.
- `_L_g_n_params` -- yes, please remove this function if you do not use
it.
Nathann
--
Ticket URL: <http://trac.sagemath.org/ticket/19418#comment:14>
Sage <http://www.sagemath.org>
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