Singular Manual: contract

  | ### 5.1.13 contract `Syntax:` `contract (` ideal_expression`,` ideal_expression `)` `Type:` matrix `Purpose:` contracts each of the n elements of the second ideal J by each of the m elements of the first ideal I, producing an matrix. Contraction is defined on monomials by: where A and B are the multiexponents of the ring variables represented by `contract` is extended bilinearly to all polynomials. `Example:`
        ring r=0,(a,b,c,d),dp;
        ideal I=a2,a2+bc,abc;
        ideal J=a2-bc,abcd;
        print(contract(I,J));
      ==> 1,0,
      ==> 0,ad,
      ==> 0,d
See diff.

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