Computing minimum_distance of a code on non-prime fields fails ... sometimes.

asked 2015-03-23 15:54:25 +0100

Koji
13 ●4

updated 2017-01-08 12:06:18 +0100

FrédéricC

5206 ●3 ●43 ●114

Consider the following piece of code:

C=codes.RandomLinearCode(4,2,GF(16,'b'))
C.minimum_distance()

About half of the time, it fails with error

TypeError: unable to coerce from a finite field other than the prime subfield

I'd understand if SAGE could only compute the minimum distance for codes over primes fields, what has me confused is the fact that sometimes it can, sometimes it can't. Any clues as to what is going on here?

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Hello,

Which version are you using? On both sage-6.5 and sage-6.6.rc0 I got

sage: C=codes.RandomLinearCode(4,2,GF(16,'b'))
sage: C.minimum_distance()
3

vdelecroix ( 2015-03-23 23:33:29 +0100 )edit

Yes, it may work for a few times; but if you keep evaluating, after a couple of successful evaluations you'll come up with a TypeError. You can try it this way, which certainly fails:

for i in range(100):
    C=codes.RandomLinearCode(4,2,GF(16,'b'))
    C.minimum_distance()

Thanks though for the interest, @vdelecroix

Koji ( 2015-03-24 20:06:02 +0100 )edit

@Koji, all right. Got the error as well!

vdelecroix ( 2015-03-24 21:10:24 +0100 )edit

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sage: K = GF(8,'a') sage: for x in K: ....: print x == K(x._gap_()), True True True True True True True True sage: K = GF(16,'a') sage: for x in K: ....: print x == K(x._gap_()), True True True True True Traceback (most recent call last): ... TypeError: unable to coerce from a finite field other than the prime subfield

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Thanks a lot for both the quick answer and the ticket. Do I get bragging rights (for my students) for uncovering this, @vdelecroix ? ;)

Koji ( 2015-03-25 09:27:33 +0100 )edit

Hopefully, Peter Bruin came with a solution to fix the bug (you can have a look on the ticket #18048. So it should be fixed in sage-6.6. In the mean time, the only solution I see is to use git to get his modifications on your computer (you do have explanations in the Developer Guide. If you are not familiar with that it might be simpler to just wait for sage-6.6 (should be a matter of weeks).

vdelecroix ( 2015-03-25 23:20:10 +0100 )edit

You guys rock! I can git my way, if my life depends on it, but since it's not "mission critical", I'll wait for 6.6.

Koji ( 2015-03-26 12:57:47 +0100 )edit

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Computing minimum_distance of a code on non-prime fields fails ... sometimes.

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