m should be a monomial map between rings created by buildERing. Such a map can be constructed with buildEMonomialMap but this is not required.
For a map to ring R from ring S, the algorithm infers the entire equivariant map from where m sends the variable orbit generators of S. In particular for each orbit of variables of the form x_{(i_1,...,i_k)}, the image of x_{(0,...,k-1)} is used.
egbToric uses an incremental strategy, computing Gröbner bases for truncations using FourTiTwo. Because of FourTiTwo's efficiency, this strategy tends to be much faster than general equivariant Gröbner basis algorithms such as egb.
In the following example we compute an equivariant Gröbner basis for the vanishing equations of the second Veronese of P^n, i.e. the variety of n x n rank 1 symmetric matrices.
i1 : R = buildERing({symbol x}, {1}, QQ, 2);
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i2 : S = buildERing({symbol y}, {2}, QQ, 2);
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i3 : m = buildEMonomialMap(R,S,{x_0*x_1})
2 2
o3 = map (R, S, {x , x x , x x , x })
1 1 0 1 0 0
o3 : RingMap R <--- S
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i4 : G = egbToric(m, OutFile=>stdio)
3
-- used .00213297 seconds
-- used .000268403 seconds
(9, 9)
new stuff found
4
-- used .00412941 seconds
-- used .00176689 seconds
(16, 26)
new stuff found
5
-- used .00932041 seconds
-- used .00665851 seconds
(25, 60)
6
-- used .0226463 seconds
-- used .0181489 seconds
(36, 120)
7
-- used .0492787 seconds
-- used .0606655 seconds
(49, 217)
2
o4 = {- y + y , - y y + y , - y y + y y , - y y +
1,0 0,1 1,1 0,0 1,0 2,1 0,0 2,0 1,0 2,1 1,0
------------------------------------------------------------------------
y y , - y y + y y , - y y + y y , - y y +
2,0 1,1 2,2 1,0 2,1 2,0 3,2 1,0 3,0 2,1 3,2 1,0
------------------------------------------------------------------------
y y }
3,1 2,0
o4 : List
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It is not checked if m is equivariant. Only the images of the orbit generators of the source ring are examined and the rest of the map ignored.
The object egbToric is a method function with options.