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D.15.1.19 arrRestrict
Procedure from library arr.lib (see arr_lib).
- Return:
- arr: the restricted hyperplane Arrangement (A^X)
- Note:
- A has to be non-empty.
- Remarks:
- We restrict A to the flat X, defined by the equations in A[v].
The restriction will only be performed, if the ideal defining
the flat X is monomial (i.e. X is an intersection of coordinate planes).
If the optional argument CC is given, the arrangement is transformed
in such a way that X has the above form.
Example:
| | LIB "arr.lib";
ring S = 0,(x,y,z),dp;
arr A = arrTypeB(3);
A;
==> _[1]=x-y
==> _[2]=x+y
==> _[3]=x-z
==> _[4]=x+z
==> _[5]=x
==> _[6]=y-z
==> _[7]=y+z
==> _[8]=y
==> _[9]=z
==>
arrRestrict(A,9);
==> _[1]=x-y
==> _[2]=x+y
==> _[3]=x
==> _[4]=y
==>
arrRestrict(A,4,"CC");
==> _[1]=1/2y-z
==> _[2]=1/2y+z
==> _[3]=y
==> _[4]=z
==>
intvec v=5,8;
arrRestrict(A,v);
==> _[1]=-z
==>
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See also:
arrCone;
arrDecone;
arrEssentialize;
arrIsEssential;
arrRestrict.
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