<p>We introduce and investigate a family of MacMahon-type <i>q</i>-series <Equation ID="Equ8"> <EquationSource Format="TEX">\( H_k^{\pm }(q)=\sum _{n=0}^{\infty } h_k^{\pm }(n)q^n=\sum _{1 \le n_1 \le \dots \le n_k} \prod _{i=1}^k \frac{q^{n_i}}{1 \mp q^{n_i}}, \)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msubsup> <mi>H</mi> <mi>k</mi> <mo>±</mo> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <munderover> <mo>∑</mo> <mrow> <mi>n</mi> <mo>=</mo> <mn>0</mn> </mrow> <mi>∞</mi> </munderover> <msubsup> <mi>h</mi> <mi>k</mi> <mo>±</mo> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> <msup> <mi>q</mi> <mi>n</mi> </msup> <mo>=</mo> <munder> <mo>∑</mo> <mrow> <mn>1</mn> <mo>≤</mo> <msub> <mi>n</mi> <mn>1</mn> </msub> <mo>≤</mo> <mo>⋯</mo> <mo>≤</mo> <msub> <mi>n</mi> <mi>k</mi> </msub> </mrow> </munder> <munderover> <mo>∏</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>k</mi> </munderover> <mfrac> <msup> <mi>q</mi> <msub> <mi>n</mi> <mi>i</mi> </msub> </msup> <mrow> <mn>1</mn> <mo>∓</mo> <msup> <mi>q</mi> <msub> <mi>n</mi> <mi>i</mi> </msub> </msup> </mrow> </mfrac> <mo>,</mo> </mrow> </math></EquationSource> </Equation>which enumerate weighted partitions according to a fixed number of (not necessarily distinct) magnitudes. These series extend the classical generating functions for partitions with a prescribed number of distinct parts originally studied by MacMahon. Using Gaussian polynomials, we establish finite and infinite linear relations between the truncated series <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(H_{k,m}^{\pm }(q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>H</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>m</mi> </mrow> <mo>±</mo> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> and their limiting forms <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(H_k^{\pm }(q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>H</mi> <mi>k</mi> <mo>±</mo> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. In particular, we derive inversion formulas expressing <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(H_k^{\pm }(q)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>H</mi> <mi>k</mi> <mo>±</mo> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> in terms of the <i>q</i>-products <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\((\pm q;q)_\infty \, q^k/(q;q)_k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mo stretchy="false">(</mo> <mo>±</mo> <mi>q</mi> <mo>;</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mi>∞</mi> </msub> <mspace width="0.166667em" /> <msup> <mi>q</mi> <mi>k</mi> </msup> <mo stretchy="false">/</mo> <msub> <mrow> <mo stretchy="false">(</mo> <mi>q</mi> <mo>;</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mi>k</mi> </msub> </mrow> </math></EquationSource> </InlineEquation>. These identities lead to new combinatorial interpretations for the coefficients of <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\((\pm q;q)_\infty \, q^k/(q;q)_k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mrow> <mo stretchy="false">(</mo> <mo>±</mo> <mi>q</mi> <mo>;</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mi>∞</mi> </msub> <mspace width="0.166667em" /> <msup> <mi>q</mi> <mi>k</mi> </msup> <mo stretchy="false">/</mo> <msub> <mrow> <mo stretchy="false">(</mo> <mi>q</mi> <mo>;</mo> <mi>q</mi> <mo stretchy="false">)</mo> </mrow> <mi>k</mi> </msub> </mrow> </math></EquationSource> </InlineEquation> in terms of signed counts of partitions, overpartitions and partition pairs. Several applications to explicit formulas for the partition functions <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(h_k^{\pm }(n)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>h</mi> <mi>k</mi> <mo>±</mo> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>n</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> are also obtained.</p>

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Family of MacMahon-type q-series and their combinatorial interpretations

  • Mircea Merca

摘要

We introduce and investigate a family of MacMahon-type q-series \( H_k^{\pm }(q)=\sum _{n=0}^{\infty } h_k^{\pm }(n)q^n=\sum _{1 \le n_1 \le \dots \le n_k} \prod _{i=1}^k \frac{q^{n_i}}{1 \mp q^{n_i}}, \) H k ± ( q ) = n = 0 h k ± ( n ) q n = 1 n 1 n k i = 1 k q n i 1 q n i , which enumerate weighted partitions according to a fixed number of (not necessarily distinct) magnitudes. These series extend the classical generating functions for partitions with a prescribed number of distinct parts originally studied by MacMahon. Using Gaussian polynomials, we establish finite and infinite linear relations between the truncated series \(H_{k,m}^{\pm }(q)\) H k , m ± ( q ) and their limiting forms \(H_k^{\pm }(q)\) H k ± ( q ) . In particular, we derive inversion formulas expressing \(H_k^{\pm }(q)\) H k ± ( q ) in terms of the q-products \((\pm q;q)_\infty \, q^k/(q;q)_k\) ( ± q ; q ) q k / ( q ; q ) k . These identities lead to new combinatorial interpretations for the coefficients of \((\pm q;q)_\infty \, q^k/(q;q)_k\) ( ± q ; q ) q k / ( q ; q ) k in terms of signed counts of partitions, overpartitions and partition pairs. Several applications to explicit formulas for the partition functions \(h_k^{\pm }(n)\) h k ± ( n ) are also obtained.