Singular Manual: toric_std

| #### D.4.35.2 toric_std Procedure from library `toric.lib` (see toric_lib). Usage: toric_std(I); I ideal Return: ideal: standard basis of I Note: This procedure computes the standard basis of I using a specialized Buchberger algorithm. The generating system by which I is given has to consist of binomials of the form x^u-x^v. There is no real check if I is toric. If I is generated by binomials of the above form, but not toric, toric_std computes an ideal `between' I and its saturation with respect to all variables. For the mathematical background, see Toric ideals and integer programming. Example:
    LIB "toric.lib";
    ring r=0,(x,y,z),wp(3,2,1);
    // call with toric ideal (of the matrix A=(1,1,1))
    ideal I=x-y,x-z;
    ideal J=toric_std(I);
    J;
    ==> J[1]=y-z
    ==> J[2]=x-z
    // call with the same ideal, but badly chosen generators:
    // 1) not only binomials
    I=x-y,2x-y-z;
    J=toric_std(I);
    ==>    ? Generator 2 of the input ideal is no difference of monomials.
    ==>    ? leaving toric.lib::toric_std (0)
    // 2) binomials whose monomials are not relatively prime
    I=x-y,xy-yz,y-z;
    J=toric_std(I);
    ==> Warning: The monomials of generator 2 of the input ideal are not relative\
       ly prime.
    J;
    ==> J[1]=y-z
    ==> J[2]=x-z
    // call with a non-toric ideal that seems to be toric
    I=x-yz,xy-z;
    J=toric_std(I);
    J;
    ==> J[1]=y2-1
    ==> J[2]=x-yz
    // comparison with real standard basis and saturation
    ideal H=std(I);
    H;
    ==> H[1]=x-yz
    ==> H[2]=y2z-z
    LIB "elim.lib";
    sat_with_exp(H,xyz);
    ==> [1]:
    ==>    _[1]=x-yz
    ==>    _[2]=y2-1
    ==> [2]:
    ==>    1
See also: Toric ideals; intprog_lib; toric_ideal; toric_lib.

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