<p>Let <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(S=K[x_1, \ldots ,x_n]\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>S</mi> <mo>=</mo> <mi>K</mi> <mo stretchy="false">[</mo> <msub> <mi>x</mi> <mn>1</mn> </msub> <mo>,</mo> <mo>…</mo> <mo>,</mo> <msub> <mi>x</mi> <mi>n</mi> </msub> <mo stretchy="false">]</mo> </mrow> </math></EquationSource> </InlineEquation> denote the polynomial ring in <i>n</i> variables over a field <i>K</i> and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(I \subset S\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>I</mi> <mo>⊂</mo> <mi>S</mi> </mrow> </math></EquationSource> </InlineEquation> a monomial ideal. Given a vector <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\mathfrak {c}\in {\mathbb {N}}^n\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="fraktur">c</mi> <mo>∈</mo> <msup> <mrow> <mi mathvariant="double-struck">N</mi> </mrow> <mi>n</mi> </msup> </mrow> </math></EquationSource> </InlineEquation>, the ideal <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(I_{\mathfrak {c}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>I</mi> <mi mathvariant="fraktur">c</mi> </msub> </math></EquationSource> </InlineEquation> is the ideal generated by those monomials belonging to <i>I</i> whose exponent vectors are componentwise bounded above by <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\mathfrak {c}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="fraktur">c</mi> </math></EquationSource> </InlineEquation>. Let <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\delta _{\mathfrak {c}}(I)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>δ</mi> <mi mathvariant="fraktur">c</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>I</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> be the largest integer <i>q</i> for which <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\((I^q)_{\mathfrak {c}}\ne 0\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mo stretchy="false">(</mo> <msup> <mi>I</mi> <mi>q</mi> </msup> <mo stretchy="false">)</mo> </mrow> <mi mathvariant="fraktur">c</mi> </msub> <mo>≠</mo> <mn>0</mn> </mrow> </math></EquationSource> </InlineEquation>. For a finite graph <i>G</i>, its edge ideal is denoted by <i>I</i>(<i>G</i>). Let <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\mathcal {B}(\mathfrak {c},G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="fraktur">c</mi> <mo>,</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> be the toric ring which is generated by the monomials belonging to the minimal system of monomial generators of <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\((I(G)^{\delta _{\mathfrak {c}}(I)})_{\mathfrak {c}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">(</mo> <mi>I</mi> <msup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <msub> <mi>δ</mi> <mi mathvariant="fraktur">c</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>I</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </msup> <mo stretchy="false">)</mo> </mrow> <mi mathvariant="fraktur">c</mi> </msub> </math></EquationSource> </InlineEquation>. In a previous work, the authors proved that <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\((I(G)^{\delta _{\mathfrak {c}}(I)})_{\mathfrak {c}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mo stretchy="false">(</mo> <mi>I</mi> <msup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mrow> <msub> <mi>δ</mi> <mi mathvariant="fraktur">c</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>I</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </msup> <mo stretchy="false">)</mo> </mrow> <mi mathvariant="fraktur">c</mi> </msub> </math></EquationSource> </InlineEquation> is a polymatroidal ideal. It follows that <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\mathcal {B}(\mathfrak {c},G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="fraktur">c</mi> <mo>,</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a normal Cohen–Macaulay domain. In this paper, we study the Gorenstein property of <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\mathcal {B}(\mathfrak {c},G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi mathvariant="script">B</mi> <mo stretchy="false">(</mo> <mi mathvariant="fraktur">c</mi> <mo>,</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>.</p>

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Bounded powers of edge ideals: Gorenstein toric rings

  • Takayuki Hibi,
  • Seyed Amin Seyed Fakhari

摘要

Let \(S=K[x_1, \ldots ,x_n]\) S = K [ x 1 , , x n ] denote the polynomial ring in n variables over a field K and \(I \subset S\) I S a monomial ideal. Given a vector \(\mathfrak {c}\in {\mathbb {N}}^n\) c N n , the ideal \(I_{\mathfrak {c}}\) I c is the ideal generated by those monomials belonging to I whose exponent vectors are componentwise bounded above by \(\mathfrak {c}\) c . Let \(\delta _{\mathfrak {c}}(I)\) δ c ( I ) be the largest integer q for which \((I^q)_{\mathfrak {c}}\ne 0\) ( I q ) c 0 . For a finite graph G, its edge ideal is denoted by I(G). Let \(\mathcal {B}(\mathfrak {c},G)\) B ( c , G ) be the toric ring which is generated by the monomials belonging to the minimal system of monomial generators of \((I(G)^{\delta _{\mathfrak {c}}(I)})_{\mathfrak {c}}\) ( I ( G ) δ c ( I ) ) c . In a previous work, the authors proved that \((I(G)^{\delta _{\mathfrak {c}}(I)})_{\mathfrak {c}}\) ( I ( G ) δ c ( I ) ) c is a polymatroidal ideal. It follows that \(\mathcal {B}(\mathfrak {c},G)\) B ( c , G ) is a normal Cohen–Macaulay domain. In this paper, we study the Gorenstein property of \(\mathcal {B}(\mathfrak {c},G)\) B ( c , G ) .