This is now ticket #18374
El miércoles, 6 de mayo de 2015, 17:47:54 (UTC+2), Jakob Kroeker escribió:
>
> It is definitely a bug in the dimension method.
>>
>
> could you open a ticket and post the link here?
>
> Am Sonntag, 3. Mai 2015 15:25:13 UTC+2 schrieb mmarco:
>>
>> It is definitely a bug in the dimension method.
>>
>> If singular can handle the ring, sage asks singular to compute the
>> dimension, which does correctly (the -1 is the singular convention for
>> empty varieties).
>>
>> The problem is that when the field is not supported by singular (which
>> happens with QQbar or finite fields of characteristic bigger than 2^31) ,
>> then sage falls back to its own toy implementation. In that case, it
>> appears that the empty case is not treated separatedly than the zero
>> dimensional case.
>>
>>
>>
>> El viernes, 1 de mayo de 2015, 21:18:55 (UTC+2), gjorgen...@my.fit.edu
>> escribió:
>>>
>>> Hi,
>>>
>>> For the following ideal, dimension() returns 0,
>>> {{{
>>> R.<s0,s1>=QQbar[]
>>> I=R.ideal([ s0 + 1, s0*s1 + s0 + s1 + 1, (-2)*s0 + 1, (-10)*s1 + 5,
>>> 5*s0^2 + 10*s0*s1 ])
>>> I.dimension()
>>> }}}
>>> but its variety is empty.
>>>
>>> Also for any other ring, dimension() returns -1 for this ideal. Is this
>>> a bug with dimension()? The documentation for dimension() doesn't seem to
>>> mention the -1 case.
>>> It provides the following example,
>>> {{{
>>> R.<x,y> = PolynomialRing(GF(2147483659),order='lex')
>>> I = R.ideal([x*y,x*y+1])
>>> I.dimension()
>>> }}}
>>> which yields dimension 0 for the ideal, yet the corresponding variety is
>>> empty.
>>>
>>> What is the expected behavior for dimension()? When the variety of the
>>> ideal in question has no points is dimension() always supposed to return -1?
>>>
>>
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