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); |
i2 : S = buildERing({symbol y}, {2}, QQ, 2); |
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 |
i4 : G = egbToric(m, OutFile=>stdio) 3 -- used .00343635 seconds -- used .000316725 seconds (9, 9) new stuff found 4 -- used .00566955 seconds -- used .00207165 seconds (16, 26) new stuff found 5 -- used .0118035 seconds -- used .00795152 seconds (25, 60) 6 -- used .0248058 seconds -- used .0212362 seconds (36, 120) 7 -- used .0615363 seconds -- used .110304 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 |
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.