#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 ncohen):
Yo,
> oops, this won't fly. The problem is that once a skew-Hadamard matrix
was de-skewed (e.g. by the usual normalization procedure, producing the
1st row and column of 1s),
> there is no general way known to make it skew again.
> (and in fact not every Hadamard matrix can be made skew, AFAIK).
>
> That is, I have to disable normalization right at the point it is done
in `hadamard_matrix_paleyI`. (writing an ad hoc code to undo this specific
normalization seems silly).
I cannot say that I understand what you have in mind, but as long as what
happens is made clear in the documentation I guess that it is okay.
> 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
Then create H-I, but don't create -S nor S.T.
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/19418#comment:20>
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