#19418: skew-Hadamard matrices and related srg's
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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: |
#19309 |
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Comment (by dimpase):
Replying to [comment:14 ncohen]:
> 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.
this won't fly either, as a skew Hadamard matrix H is not skew-symmetric.
What is skew-symmetric is the matrix H-I, so it has to be created anyway
(by the way, this explains why making a Hadamard matrix skew is not too
obvious; indeed,
the trick mentioned in the docs of `is_skew_symmetrizable` would only work
if H had
constant diagonal.)
--
Ticket URL: <http://trac.sagemath.org/ticket/19418#comment:19>
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