Re: riemann roch basis

[Slumberland]

Ah.  That is a confusing error message.

AttributeError: 'ProjectiveCurve_finite_field' object has no attribute 'riemann_roch_basis'

... because the size of the finite_field F is not prime.

According to the documentation

To compute a basis of the Riemann-Roch space of a divisor  on a curve over a field , one can use Sage’s wrapper riemann_roch_basis of Singular’s implementation of the Brill Noether algorithm. Note that this wrapper currently only works when  is prime and the divisor  is supported on rational points.

Your example gave me the same error.  I then tried the example on the documentation page, (Field size = 5) and it worked, so it appears this information is still accurate.

I don't see any problem with the way you defined w, but I could be wrong. This math is still new to me.

Good luck.

On Tuesday, June 12, 2012 8:20:04 PM UTC-7, Gato wrote:

hello! i have a question with this code (i speak little english)

F.<w>=GF(4,'w')
R.<X,Y,Z> = ProjectiveSpace(F,2)
C = Curve(X^2*Y + w*Y^2*Z+ w^2*Z^2*X)
print C
print C.genus()
pts = C.rational_points()
print pts[4]
print pts[5]
D = C.divisor([ (2, pts[4]),(1, pts[5]) ])
print D
print C.riemann_roch_basis(D)

result:

Projective Curve over Finite Field in w of size 2^2 defined by X^2*Y + (w)*Y^2*Z + (w + 1)*X*Z^2
1
(1 : w : 1)
(w : 1 : 1)
2*(X + Z, Y + (w)*Z) + (X + (w)*Z, Y + Z)
Traceback (most recent call last):    print pts[4]
  File "", line 1, in <module>
   
  File "/tmp/tmpkLnPnU/___code___.py", line 13, in <module>
    exec compile(u'print C.riemann_roch_basis(D)
  File "", line 1, in <module>
   
  File "parent.pyx", line 871, in sage.structure.parent.Parent.__getattr__ (sage/structure/parent.c:6648)
AttributeError: 'ProjectiveCurve_finite_field' object has no attribute 'riemann_roch_basis'

why?

I think the problem is in the function w associated to the curve