ApCoCoA-1:Num.SubABM
Num.SubABM
Computes a border basis of an almost vanishing sub-ideal for a set of points and an ideal using the Num.ABM algorithm.
Syntax
Num.SubABM(Points:MAT, Tau:RAT, GBasis:LIST):Object Num.SubABM(Points:MAT, Tau:RAT, GBasis:LIST, Delta:RAT, NormalizeType:INT):Object
Description
Please note: The function(s) explained on this page is/are using the ApCoCoAServer. You will have to start the ApCoCoAServer in order to use it/them.
This command computes a border basis of an almost vanishing sub-ideal for a set of points and an ideal using the Num.ABM algorithm.
The current ring has to be a ring over the rational numbers with a standard-degree
compatible term-ordering. Each row in the matrix Points represents one point, so the number of columns must equal the
number of indeterminates in the current ring.
@param Points The points for which a border basis is computed.
@param Tau A positive rational number describing which singular values should be treated as 0 (smaller values for tau lead to bigger errors of the polynomials evaluated at the point set). Tau should be in the interval (0,1). As a rule of thumb, Tau is the expected percentage of error on the input points.
@param GBasis A homogeneous Groebner Basis in the current ring. This basis defines the ideal in which we compute the basis of the approximate vanishing ideal. Warning: For reasons of efficiency the function does not check the validity of GBasis.
@return A list of two results. First the border basis as a list of polynomials, second the vector space basis of P/I as a list of terms.
The following parameters are optional:
@param Delta A positive rational number which describes the computing precision. In different steps, it is crucial, if a value is 0 or not. The algorithm assumes every value in [-Delta, Delta] to be 0. The default value for Delta is 0.00000000001.
@param NormalizeType A integer of the set {1,2,3,4}. The default value is 2. This parameter describes, if and where required the input points are normalized. If NormalizeType equals 1, each coordinate of a point is divided by the maximal absolute value of all coordinates of this point. This ensures that all coordinates of the points are within [-1,1]. With NormalizeType=2 no normalization is done at all. NormalizeType=3 shifts each coordinate to [-1,1], i.e. the minimal coordinate of a point is mapped to -1 and the maximal coordinate to 1, which describes a unique affine mapping. The last option is NormalizeType=4. In this case, each point is normalized by its euclidean norm. Although NormalizeType=3 is in most cases a better choice, the default value is due to backward compatibility 1.
Example
Use P::=QQ[x,y,z]; Points := Mat([[2/3,0,0],[0,1,0],[0,0,1/3]]); R:=Num.SubABM(Points, 0.1, [1,x]); Dec(R[1],2); R[2]; -- CoCoAServer: computing Cpu Time = 0.015 ------------------------------- [<quotes>0.41 x +0.27 y +0.82 z -0.27 </quotes>, <quotes>0.94 z^2 -0.31 z -0.00 </quotes>, <quotes>1 yz </quotes>, <quotes>1 xz </quotes>, <quotes>0.70 y^2 -0.70 y -0.00 </quotes>, <quotes>1 xy </quotes>] ------------------------------- [1, z, y] -------------------------------
See also
