<p>A set of vertices <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(X\subseteq V(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>X</mi> <mo>⊆</mo> <mi>V</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation> is a <i>d</i>-distance dominating set if for every <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(u\in V(G)\setminus X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>u</mi> <mo>∈</mo> <mi>V</mi> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> <mo lspace="0.15em" rspace="0.15em" stretchy="false">\</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> there exists <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(x\in X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>x</mi> <mo>∈</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation> such that <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(d(u,x) \le d\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>d</mi> <mo stretchy="false">(</mo> <mi>u</mi> <mo>,</mo> <mi>x</mi> <mo stretchy="false">)</mo> <mo>≤</mo> <mi>d</mi> </mrow> </math></EquationSource> </InlineEquation>, and <i>X</i> is a <i>p</i>-packing if <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(d(u,v) \ge p+1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>d</mi> <mo stretchy="false">(</mo> <mi>u</mi> <mo>,</mo> <mi>v</mi> <mo stretchy="false">)</mo> <mo>≥</mo> <mi>p</mi> <mo>+</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> for every different <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(u,v\in X\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>u</mi> <mo>,</mo> <mi>v</mi> <mo>∈</mo> <mi>X</mi> </mrow> </math></EquationSource> </InlineEquation>. The <i>d</i>-distance <i>p</i>-packing domination number <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\gamma _d^p(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mi>d</mi> <mi>p</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of <i>G</i> is the minimum size of a set of vertices of <i>G</i> which is both a <i>d</i>-distance dominating set and a <i>p</i>-packing. It is proved that for every two fixed integers <i>d</i> and <i>p</i> with <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(2 \le d\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>2</mn> <mo>≤</mo> <mi>d</mi> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(0 \le p \le 2d-1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>0</mn> <mo>≤</mo> <mi>p</mi> <mo>≤</mo> <mn>2</mn> <mi>d</mi> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, the decision problem whether <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\gamma _d^p(G) \le k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mi>d</mi> <mi>p</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mi>k</mi> </mrow> </math></EquationSource> </InlineEquation> holds is NP-complete for bipartite planar graphs. A necessary and sufficient condition for the existence of a <i>d</i>-distance <i>p</i>-packing dominating set in <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(C_n\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>C</mi> <mi>n</mi> </msub> </math></EquationSource> </InlineEquation> is obtained and <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\gamma _d^p(C_n)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mi>d</mi> <mi>p</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <msub> <mi>C</mi> <mi>n</mi> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> determined for every <i>d</i>, <i>p</i>, and <i>n</i>. For a tree <i>T</i> on <i>n</i> vertices with <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(\ell \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>ℓ</mi> </math></EquationSource> </InlineEquation> leaves and <i>s</i> support vertices it is proved that (i) <InlineEquation ID="IEq14"> <EquationSource Format="TEX">\(\gamma _2^0(T) \ge \frac{n-\ell -s+4}{5}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mn>2</mn> <mn>0</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> <mo>≥</mo> <mfrac> <mrow> <mi>n</mi> <mo>-</mo> <mi>ℓ</mi> <mo>-</mo> <mi>s</mi> <mo>+</mo> <mn>4</mn> </mrow> <mn>5</mn> </mfrac> </mrow> </math></EquationSource> </InlineEquation>, (ii) <InlineEquation ID="IEq15"> <EquationSource Format="TEX">\(\lceil \frac{n-\ell -s+4}{5} \rceil \le \gamma _2^2(T) \le \left\lfloor \frac{n+3s-1}{5} \right\rfloor \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo>⌈</mo> <mfrac> <mrow> <mi>n</mi> <mo>-</mo> <mi>ℓ</mi> <mo>-</mo> <mi>s</mi> <mo>+</mo> <mn>4</mn> </mrow> <mn>5</mn> </mfrac> <mo>⌉</mo> </mrow> <mo>≤</mo> <msubsup> <mi>γ</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mfenced close="⌋" open="⌊"> <mfrac> <mrow> <mi>n</mi> <mo>+</mo> <mn>3</mn> <mi>s</mi> <mo>-</mo> <mn>1</mn> </mrow> <mn>5</mn> </mfrac> </mfenced> </mrow> </math></EquationSource> </InlineEquation>, and if <InlineEquation ID="IEq16"> <EquationSource Format="TEX">\(d \ge 2\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>d</mi> <mo>≥</mo> <mn>2</mn> </mrow> </math></EquationSource> </InlineEquation>, then (iii) <InlineEquation ID="IEq17"> <EquationSource Format="TEX">\(\gamma _d^2(T) \le \frac{n-2\sqrt{n}+d+1}{d}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mi>d</mi> <mn>2</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mfrac> <mrow> <mi>n</mi> <mo>-</mo> <mn>2</mn> <msqrt> <mi>n</mi> </msqrt> <mo>+</mo> <mi>d</mi> <mo>+</mo> <mn>1</mn> </mrow> <mi>d</mi> </mfrac> </mrow> </math></EquationSource> </InlineEquation>. Inequality (i) improves an earlier bound due to Meierling and Volkmann, and independently Raczek, Lemańska, and Cyman, while (iii) extends an earlier result for <InlineEquation ID="IEq18"> <EquationSource Format="TEX">\(\gamma _2^2(T)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> due to Henning. Sharpness of the bounds is discussed and established in most cases. It is also proved that every connected graph <i>G</i> contains a spanning tree <i>T</i> such that <InlineEquation ID="IEq19"> <EquationSource Format="TEX">\(\gamma _2^2(T) \le \gamma _2^2(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>γ</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <msubsup> <mi>γ</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>.</p>

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The d-distance p-packing domination number: complexity, cycles, and trees

  • Csilla Bujtás,
  • Vesna Iršič Chenoweth,
  • Sandi Klavžar,
  • Gang Zhang

摘要

A set of vertices \(X\subseteq V(G)\) X V ( G ) is a d-distance dominating set if for every \(u\in V(G)\setminus X\) u V ( G ) \ X there exists \(x\in X\) x X such that \(d(u,x) \le d\) d ( u , x ) d , and X is a p-packing if \(d(u,v) \ge p+1\) d ( u , v ) p + 1 for every different \(u,v\in X\) u , v X . The d-distance p-packing domination number \(\gamma _d^p(G)\) γ d p ( G ) of G is the minimum size of a set of vertices of G which is both a d-distance dominating set and a p-packing. It is proved that for every two fixed integers d and p with \(2 \le d\) 2 d and \(0 \le p \le 2d-1\) 0 p 2 d - 1 , the decision problem whether \(\gamma _d^p(G) \le k\) γ d p ( G ) k holds is NP-complete for bipartite planar graphs. A necessary and sufficient condition for the existence of a d-distance p-packing dominating set in \(C_n\) C n is obtained and \(\gamma _d^p(C_n)\) γ d p ( C n ) determined for every d, p, and n. For a tree T on n vertices with \(\ell \) leaves and s support vertices it is proved that (i) \(\gamma _2^0(T) \ge \frac{n-\ell -s+4}{5}\) γ 2 0 ( T ) n - - s + 4 5 , (ii) \(\lceil \frac{n-\ell -s+4}{5} \rceil \le \gamma _2^2(T) \le \left\lfloor \frac{n+3s-1}{5} \right\rfloor \) n - - s + 4 5 γ 2 2 ( T ) n + 3 s - 1 5 , and if \(d \ge 2\) d 2 , then (iii) \(\gamma _d^2(T) \le \frac{n-2\sqrt{n}+d+1}{d}\) γ d 2 ( T ) n - 2 n + d + 1 d . Inequality (i) improves an earlier bound due to Meierling and Volkmann, and independently Raczek, Lemańska, and Cyman, while (iii) extends an earlier result for \(\gamma _2^2(T)\) γ 2 2 ( T ) due to Henning. Sharpness of the bounds is discussed and established in most cases. It is also proved that every connected graph G contains a spanning tree T such that \(\gamma _2^2(T) \le \gamma _2^2(G)\) γ 2 2 ( T ) γ 2 2 ( G ) .