add support for weight vectors to gran/groebner_fan

[sagetrac-mhampton]

This should be pretty straightforward.

sage-support request from Ursula Whitcher:
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

Component: interfaces

Keywords: gfan, groebner_fan, weight vectors

Issue created by migration from https://trac.sagemath.org/ticket/4352

[sagetrac-mhampton]

Attachment: 4352_1.patch.gz

based on 3.1.4 but should be fine against 3.2-alpha0

[williamstein]

comment:2

REVIEW:

patch applies and passes test. Code raises major red flag!!

	        ans = eval(ans.replace('{','').replace('}','').replace('\n','')) 

If the output -- which you make into vectors over QQ ever actually has any rational numbers, then eval will do very bad things to them, e.g.,

sage: eval('2/3')
0

Oops!

Use sage_eval instead:

sage: sage_eval('2/3')
2/3

[sagetrac-mhampton]

Attachment: 4352_2.patch.gz

supercedes previous patch, addresses review

[sagetrac-mabshoff]

comment:5

This patch no longer applies cleanly to my 3.2.1.rc1 merge tree:

sage-3.2.1.rc1/devel/sage$ patch -p1 --dry-run < trac_4352_2.patch 
patching file sage/rings/polynomial/groebner_fan.py
Hunk #2 FAILED at 76.
1 out of 3 hunks FAILED -- saving rejects to file sage/rings/polynomial/groebner_fan.py.rej

I gather from the patch description that only trac_4352_2.patch should be applied. So unless I am mistaken please rebase this. If there are unknown dependencies for this ticket please list them.

Cheers,

Michael

[sagetrac-mhampton]

Attachment: 4352_3.patch.gz

rebased against 3.2.1.rc0

[sagetrac-mabshoff]

comment:7

Merged 4352_3.patch in Sage 3.2.1.rc1