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D.15.16.7 GITfan

Procedure from library gitfan.lib (see gitfan_lib).

Usage:
GITfan(J,Q [, G]); J:ideal, Q:intmat, G:list

Purpose:
Computes the GIT fan associated to J and Q. Optionally a symmetry group action on the column space of Q can be specified.

Return:
a fan, the GIT fan.

Note:
The proceduce uses parallel computation for the construction of the GIT-cones. The a-faces are not computed in parallel. This can be done by calling the aface procedure specifying a list of simplex faces. If used with the optional argument G, the orbit decomposition of the simplex of columns of Q is computed. Refer to the Singular documentation on how to do this more efficiently using GAP.

Example:
 
LIB "gitfan.lib";
setcores(4);
==> 4
ring R = 0,T(1..10),wp(1,1,1,1,1,1,1,1,1,1);
ideal J =
T(5)*T(10)-T(6)*T(9)+T(7)*T(8),
T(1)*T(9)-T(2)*T(7)+T(4)*T(5),
T(1)*T(8)-T(2)*T(6)+T(3)*T(5),
T(1)*T(10)-T(3)*T(7)+T(4)*T(6),
T(2)*T(10)-T(3)*T(9)+T(4)*T(8);
intmat Q[5][10] =
1, 1, 1, 1, 0, 0, 0, 0, 0, 0,
1, 0, 0, 0, 1, 1, 1, 0, 0, 0,
0, 1, 1, 0, 0, 0, -1, 1, 0, 0,
0, 1, 0, 1, 0, -1, 0, 0, 1, 0,
0, 0, 1, 1, -1, 0, 0, 0, 0, 1;
fan GIT = GITfan(J,Q);
intmat Q[5][10] =
==> // ** redefining Q (intmat Q[5][10] =)
1, 1, 1, 1, 0, 0, 0, 0, 0, 0,
1, 0, 0, 0, 1, 1, 1, 0, 0, 0,
0, 1, 1, 0, 0, 0, -1, 1, 0, 0,
0, 1, 0, 1, 0, -1, 0, 0, 1, 0,
0, 0, 1, 1, -1, 0, 0, 0, 0, 1;
list simplexSymmetryGroup = G25Action();
fan GIT2 = GITfan(J,Q,simplexSymmetryGroup);