#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: Dima | 01763fd38506f8721560fa29e60227e5081db08b
Pasechnik | Stopgaps:
Report Upstream: N/A |
Branch: |
public/19418 |
Dependencies: |
#19309 |
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Comment (by dimpase):
Replying to [comment:37 ncohen]:
> - In the `n%8==0` case you implement the product construction of skew
hadamard
> matrices with a 2x2 matrix only. Is there a reason to that?
huh? I have there
{{{
elif n % 8 == 0:
if skew_hadamard_matrix(n//2,existence=True, check=False):
if existence:
return true()
H = skew_hadamard_matrix(n//2,check=False)
M = block_matrix([[H,H], [-H.T,H.T]])
else: # try Williamson construction
for d in divisors(n)[2:-2]: # skip 1, 2, n/2, and n
... more stuff
}}}
so I first check if I can multiply with 2x2 matrix, and if not, I `try
Williamson construction`.
--
Ticket URL: <http://trac.sagemath.org/ticket/19418#comment:38>
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