Difference between revisions of "ApCoCoA-1:Num.ABM"
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This command computes a border basis of an almost vanishing ideal for a set of points. | This command computes a border basis of an almost vanishing ideal for a set of points. | ||
<par/> | <par/> | ||
| − | The current ring has to be a ring over the | + | The current ring has to be a ring over the rational numbers with a standard-degree |
| − | compatible term-ordering. | + | compatible term-ordering. The matrix <tt>Points</tt> contains the points: each |
point is a row in the matrix, so the number of columns must equal the | point is a row in the matrix, so the number of columns must equal the | ||
number of indeterminates in the current ring. | number of indeterminates in the current ring. | ||
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<item>@param <em>Points</em> The points for which a border basis is computed.</item> | <item>@param <em>Points</em> The points for which a border basis is computed.</item> | ||
| − | <item>@param <em>Tau</em> A positive rational number describing which singular values should be treated as 0 (smaller values for | + | <item>@param <em>Tau</em> A positive rational number describing which singular values should be treated as 0 (smaller values for <tt>Tau</tt> lead to bigger errors of the polynomials evaluated at the point set). <tt>Tau</tt> should be in the interval (0,1). As a rule of thumb, <tt>Tau</tt> is the expected percentage of error on the input points. </item> |
| − | |||
| − | |||
| + | <item>@return A list of two results. First the border basis as a list of polynomials, second the vector space basis of <tt>P/I</tt> as a list of terms.</item> | ||
</itemize> | </itemize> | ||
The following parameters are optional: | The following parameters are optional: | ||
<itemize> | <itemize> | ||
| − | <item>@param <em>Delta</em> A positiv rational number. Delta 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 | + | <item>@param <em>Delta</em> A positiv rational number. <tt>Delta</tt> describes the computing precision. In different steps, it is crucial, if a value is 0 or not. The algorithm assumes every value in <tt>[-Delta, Delta]</tt> to be 0. The default value for <tt>Delta</tt> is 0.00000000001.</item> |
| − | |||
| − | |||
| + | <item>@param <em>NormalizeType</em> A integer of the range 1..4. The default value is 2. This parameter describes, if/how the input points are normalized. If <tt>NormalizeType</tt> equals 1, each coordinate is divided by the maximal absolute value of the corresponding column of the matrix. This ensures that all coordinates of points are in [-1,1]. With <tt>NormalizeType=2</tt> no normalization is done at all. <tt>NormalizeType=3</tt> shifts each coordinate to [-1,1]. So it's minimum is mapped to -1 and the maximum to one, describing a unique affine mapping. The last option is <tt>NormalizeType=4</tt>. In this case, each coordinate is normalized, using the column's euclidian norm. Due to backward compatibility, the default is 1, although 3 is in most cases a better choice.</item> | ||
</itemize> | </itemize> | ||
Revision as of 14:07, 7 July 2009
Num.ABM
Computes the border basis of an almost vanishing ideal for a set of points.
Syntax
Num.ABM(Points:MAT, Tau:RAT):Object Num.ABM(Points:MAT, Tau:RAT, 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 ideal for a set of points.
The current ring has to be a ring over the rational numbers with a standard-degree
compatible term-ordering. The matrix Points contains the points: each
point is a row in the matrix, 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.
@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 positiv rational number. Delta 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 range 1..4. The default value is 2. This parameter describes, if/how the input points are normalized. If NormalizeType equals 1, each coordinate is divided by the maximal absolute value of the corresponding column of the matrix. This ensures that all coordinates of points are in [-1,1]. With NormalizeType=2 no normalization is done at all. NormalizeType=3 shifts each coordinate to [-1,1]. So it's minimum is mapped to -1 and the maximum to one, describing a unique affine mapping. The last option is NormalizeType=4. In this case, each coordinate is normalized, using the column's euclidian norm. Due to backward compatibility, the default is 1, although 3 is in most cases a better choice.
Example
Use P::=QQ[x,y,z]; Points := Mat([[1,0,0],[0,0,1],[0,0.99,0]]); Res := Num.ABM(Points,0.1); Dec(Res[1],2); -- CoCoAServer: computing Cpu Time = 0 ------------------------------- [<quotes>-0.49 x -0.50 y -0.49 z +0.49 </quotes>, <quotes>-0.70 z^2 +0.70 z -0.00 </quotes>, <quotes>1 yz </quotes>, <quotes>1 xz </quotes>, <quotes>0.71 y^2 -0.70 y -0.00 </quotes>, <quotes>1 xy </quotes>] -------------------------------
See also
