On Wed, 11 May 2011 22:57:56 -0700 (PDT)
tvn <[email protected]> wrote:
> Is this a "math" limitation or Sage limitation ? If it's the later then
> should it be worked on ?
>
> 'Sage Version 4.6.2, Release Date: 2011-02-25'
> sage: var('x x2')
> (x, x2)
> sage: Q = PolynomialRing(QQ,[x,x2])
> sage: I = Q*([x+x2])
> sage: I.gro
> I.groebner_basis I.groebner_fan
> sage: I.groebner_fan()
>
> ---------------------------------------------------------------------------
> RuntimeError Traceback (most recent call last)
>
> ......
>
> /Users/tnguyen/Src/Devel/SAGE/sage/local/lib/python2.6/site-packages/sage/rings/polynomial/groebner_fan.pyc
>
> in __init__(self, I, is_groebner_basis, symmetry, verbose)
> 453 raise TypeError, "I must be a multivariate polynomial
> ideal"
> 454 if prefix_check([str(R_gen) for R_gen in I.ring().gens()])
> != True:
> --> 455 raise RuntimeError, "Ring variables cannot contain each
> other as prefixes"
> 456 S = I.ring()
> 457 R = S.base_ring()
>
> RuntimeError: Ring variables cannot contain each other as prefixes
It is probably a limitation of the parser in gfan [1], which is the
software we use to compute groebner fans.
[1] http://www.math.tu-berlin.de/~jensen/software/gfan/gfan.html
We could change the variable names before calling gfan to work around
this. AFAIK, there is also a library interface to gfan in the making,
which probably doesn't suffer from this limitation.
Cheers,
Burcin
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