#19340: Better interface for hadamard_matrix
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Reporter: ncohen | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.9
Component: combinatorial | Resolution:
designs | Merged in:
Keywords: | Reviewers:
Authors: Nathann Cohen | Work issues:
Report Upstream: N/A | Commit:
Branch: u/ncohen/19340 | a5a4bbff80f2aed2a5b549d6b64f215967bc5ec7
Dependencies: | Stopgaps:
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Comment (by dimpase):
Replying to [comment:6 fredrik.johansson]:
> You might consider using the flint functions fmpz_mat_hadamard and
fmpz_mat_is_hadamard, which should be faster.
>
> Checking by default seems kind of useless since this is much slower than
generating the matrix (generating a size 1000 Hadamard matrix takes 0.01
seconds and checking it takes 0.5 seconds),
IMHO it says that your fmpz_mat_is_hadamard is far from optimal.
Indeed, you neither need to take the transpose nor to do full matrix
multiplication.
As you fisrt check that the matrix is +/-1, you don't need to check that
the diagonal entries of HH.T are all n.
So you only need to do scalar products of n(n-1)/2 rows...
(I understand that Hadamard matrices in FLINT don't do any serious job,
they are there for testing or so; if one was after real speed there, you'd
be using BLAS...)
--
Ticket URL: <http://trac.sagemath.org/ticket/19340#comment:18>
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