Hi Ursula,
This is not currently supported by Sage in an easy way. Since you are
interested (and I am too now), I will file a ticket for an
enhancement, but I don't have time to work on it right away.
I can give you an example of how to do it in a crude way:
r.<x,y> = PolynomialRing(QQ,2)
fg = r.ideal([x^2-y,y^4-x]).groebner_fan()
from subprocess import *
gfan_processes = Popen(['gfan','_weightvector','-m'],stdin = PIPE,
stdout=PIPE, stderr=PIPE)
ans, err = gfan_processes.communicate(input = fg.gfan())
print ans
will return
{
(5,1),
(3,1),
(1,3)}
which I presume are the weight vectors corresponding to the three
reduced Groebner bases in this example.
On Oct 23, 2:18 pm, Ursula Whitcher <[EMAIL PROTECTED]>
wrote:
> I asked Anders Jensen, "I would like to compute the weight vectors
> corresponding to each reduced Groebner basis in gfan's output. Is
> there a way to tell gfan to do this?"
>
> He replied:
>
> "There is a command "weightvector" that does exactly this. The command
> is hidden (does not show up in the manual or the file system). To run
> it type "gfan _weightvector" in your shell. MIND THE SPACE BEFORE '_'.
> According to the --help text the correct thing to do would be to run
> "gfan _weightvector -m" with the gfan output as input.
>
> For example
> gfan | gfan _weightvector -m
> Q[x,y]
> {x-y}
>
> will produce a list of two vectors.
> I hope this works out for you.
> Best regards,
> Anders"
>
> Is there a way to access the weightvector command from the Sage
> implementation of gfan?
>
> Thanks!
> Ursula
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