Syndrome decoder for a linear code sometimes sets wrong decoder type

[johanrosenkilde]

There is a bug in how the decoder type is set for the syndrome decoder. Consider

sage: C = codes.HammingCode(GF(5), 3)
sage: D = C.decoder("Syndrome")
sage: C.minimum_distance()
3
sage: D.maximum_error_weight()
1
sage: D.decoder_type()
{'complete', 'hard-decision', 'might-error', 'unique'}

The last line should not have had "might-error" but instead should have had "always-succeed" and "minimum-distance".

CC: @sagetrac-dlucas

Component: coding theory

Keywords: linear code, syndrome, rd3

Author: Clément Pernet

Branch/Commit: f152ea8

Reviewer: Bruno Grenet

Issue created by migration from https://trac.sagemath.org/ticket/20898

[ClementPernet]

Branch: u/cpernet/syndrome_decoder_type

[ClementPernet]

Author: Clément Pernet

[ClementPernet]

comment:2

There was actually 2 bugs: the decoding_radius tested for this decision was not updated with the value found during the construction of the lookup table. Then some set.add needed to be changed.

I also added the ticket's code as a doctest.

Attached branch should fix the pb. Open for review.

---

New commits:

ffb9bdc	fix 2 bugs: the updated max_error_weight was not tested + add->union
6f8bf3c	Need to get the result that union returns
d581d76	add #20898 code as a doctest

[ClementPernet]

Changed keywords from linear code, syndrome to linear code, syndrome, rd3

[ClementPernet]

Commit: d581d76

[sagetrac-git]

Changed commit from d581d76 to f152ea8

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

f152ea8

replace union by update

[bgrenet]

Reviewer: Bruno Grenet

[bgrenet]

comment:4

Looks OK!

[vbraun]

Changed branch from u/cpernet/syndrome_decoder_type to f152ea8