OK, I got a little addicted to thinking about this and did a slightly
better job. The following function will return the weight vectors as
Sage QQ vectors:
from subprocess import Popen, PIPE
def weight_vectors(a_groebner_fan):
"""
Returns the weight vectors corresponding to the reduced Groebner
bases of a groebner_fan object.
"""
gfan_processes = Popen(['gfan','_weightvector','-m'],stdin = PIPE,
stdout=PIPE, stderr=PIPE)
ans, err = gfan_processes.communicate(input =
a_groebner_fan.gfan())
ans = eval(ans.replace('{','').replace('}','').replace('\n',''))
ans = [vector(QQ,x) for x in ans]
return ans
-M. Hampton
On Oct 23, 3:19 pm, Marshall Hampton <[EMAIL PROTECTED]> wrote:
> OK, this is now trac #4352. I should be able to do this in the next
> couple of months at the latest.
>
> -Marshall Hampton
>
> On Oct 23, 3:15 pm, Marshall Hampton <[EMAIL PROTECTED]> wrote:
>
> > 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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