Utilitas Algorithmica (UA)
ISSN: xxxx-xxxx (print)
Utilitas Algorithmica (UA) is a premier, open-access international journal dedicated to advancing algorithmic research and its applications. Launched to drive innovation in computer science, UA publishes high-impact theoretical and experimental papers addressing real-world computational challenges. The journal underscores the vital role of efficient algorithm design in navigating the growing complexity of modern applications. Spanning domains such as parallel computing, computational geometry, artificial intelligence, and data structures, UA is a leading venue for groundbreaking algorithmic studies.
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 159-180
- Published: 31/05/2010
Let \((X, \mathcal{B})\) be a \(\lambda\)-fold \(G\)-decomposition of \(\lambda H\). Let \(G_i\), \(i=1,\ldots,\mu\), be all nonisomorphic proper subgraphs of \(G\) without isolated vertices. Put \(\mathcal{B}_i = \{B_i \mid B \in \mathcal{B}\}\), where \(B_i\) is a subgraph of \(B\) isomorphic to \(G_i\). A complete simultaneous metamorphosis of \((X, \mathcal{B})\) is a rearrangement, for each \(i = 1, \ldots, \mu\), of the edges of \(\bigcup_{B \in \mathcal{B}} (E(B) \setminus E(B_i))\) into a family \(\mathcal{F}_i\) of copies of \(G_i\) with a leave \(L_i\), such that \((X, \mathcal{B}_i \cup \mathcal{F}_i, L_i)\) is a maximum packing of \(\lambda H\) with copies of \(G_i\). In this paper, we give a complete answer to the existence problem of a \(\lambda\)-fold kite system having a complete simultaneous metamorphosis.
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 143-158
- Published: 31/05/2010
Whist tournaments for \( v \) players, \( \mathrm{Wh}(v) \), are known to exist for all \( v \equiv 0, 1 \pmod{4} \). In this paper, a new specialization of whist tournament design, namely a \({balanced\; whist\; tournament}\), is introduced. We establish that balanced whist tournaments on \( v \) players, \( \mathrm{BWh}(v) \), exist for several infinite classes of \( v \). An adaptation of a classic construction due to R. C. Bose and J. M. Cameron enables us to establish that \( \mathrm{BWh}(4n + 1) \) exist whenever \( 4n + 1 \) is a prime or a prime power. It is also established that \( \mathrm{BWh}(4n) \) exist for \( 4n = 2^k \), with \( k \equiv 0 \pmod{2, 3 \text{ or } 5} \). We demonstrate that a \( \mathrm{BWh}(4n + 1) \) is equivalent to a conference matrix of order \( 4n + 2 \). Consequently, a necessary condition for the existence of a \( \mathrm{BWh}(4n + 1) \) is that \( 4n + 1 \) is a product of primes each of which is \( \equiv 1 \pmod{4} \). Thus, in particular, \( \mathrm{BWh}(21) \) and \( \mathrm{BWh}(33) \) do not exist. Specific examples of \( \mathrm{BWh}(v) \) are given for \( v = 4, 8, 9, 20, 24, 32 \). It is also shown that a \( \mathrm{BWh}(12) \) does not exist.
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 135-141
- Published: 31/05/2010
Let \(\alpha(G)\) represent the maximal size of any product-free subset of a finite abelian group \(G\). It is well known that \(\alpha(G) = \frac{|G|}{3}\left(1 + \frac{1}{p}\right)\) if \(|G|\) is divisible by a prime \(p \equiv 2 \pmod{3}\) and \(p\) is the smallest such prime, \(\alpha(G) = \frac{|G|}{3}\) if \(|G|\) is not divisible by a prime \(p \equiv 2 \pmod{3}\) but \(3\) divides \(|G|\), and \(\alpha(G) = \frac{|G|}{3}\left(1 – \frac{1}{m}\right)\) if \(|G|\) is divisible only by primes \(p \equiv 1 \pmod{3}\) and \(m\) is the exponent of \(|G|\). In this paper, we use only basic group theory and number theory to derive exact expressions for the number of different maximal product-free subsets of \(G\) in the first two cases. The formulas are given in terms of the sizes of the subgroups of \(G\).
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 127-134
- Published: 31/05/2010
The \( P_3 \) intersection graph \( P_3(G) \) of a graph \( G \) is the intersection graph of all induced \( 3 \)-paths in \( G \). In this paper, we prove that any \( P_3 \)-convergent graph is \( P_3^n(G) \)-complete for some \( n \geq 1 \). Additionally, we prove that there are no \( P_3 \)-fixed graphs. The touching number, periodicity, and connectivity of \( P_3(G) \) are also studied.
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 103-125
- Published: 31/05/2010
This paper describes the study of a special class of 4-regular plane graphs that are Hamiltonian. These graphs are of particular interest in knot theory. An algorithm is presented that randomly generates such graphs with \( n \) vertices with a fixed (and oriented) Hamiltonian cycle in \( O(n) \) time. An exact count of the number of such graphs with \( n \) vertices is obtained, and the asymptotic growth rate of this number is determined. Numerical evidence is provided to show that the algorithm can be modified to generate these graphs with a near uniform probability. This can be considered a first step in generating large random knots without bias.
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 95-102
- Published: 31/05/2010
We enumerate nonisomorphic minimum genus orientable embeddings of the complete bipartite graph \( K_{m,n} \) for \( 2 \leq m, n \leq 7 \) except for \( (m, n) = (7, 7) \).
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 85-94
- Published: 31/05/2010
A complete coloring of a graph \( G \) is a proper vertex coloring of \( G \) with the property that for every two distinct colors \( i \) and \( j \) used in the coloring, there exist adjacent vertices of \( G \) colored \( i \) and \( j \). The maximum positive integer \( k \) for which \( G \) has a complete \( k \)-coloring is the achromatic number \( \psi(G) \) of \( G \).
A Grundy coloring of a graph \( G \) is a proper vertex coloring of \( G \) with the property that for every two colors (positive integers) \( i \) and \( j \) with \( i < j \), every vertex colored \( j \) has a neighbor colored \( i \). The maximum positive integer \( k \) for which a graph \( G \) has a Grundy \( k \)-coloring is the Grundy number \( \Gamma(G) \). Thus, \( 2 \leq \chi(G) \leq \Gamma(G) \leq \psi(G) \) for every nonempty graph \( G \). It is shown that if \( a, b, \) and \( c \) are integers with \( 2 \leq a \leq b \leq c \), then there exists a connected graph \( G \) with \( \chi(G) = a \), \( \Gamma(G) = b \), and \( \psi(G) = c \) if and only if \( a = b = c = 2 \) or \( b \geq 3 \).
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 77-84
- Published: 31/05/2010
A complete coloring of a graph \( G \) is a proper vertex coloring of \( G \) with the property that for every two distinct colors \( i \) and \( j \) used in the coloring, there exist adjacent vertices of \( G \) colored \( i \) and \( j \). The maximum positive integer \( k \) for which \( G \) has a complete \( k \)-coloring is the achromatic number \( \psi(G) \) of \( G \).
A Grundy coloring of a graph \( G \) is a proper vertex coloring of \( G \) with the property that for every two colors (positive integers) \( i \) and \( j \) with \( i < j \), every vertex colored \( j \) has a neighbor colored \( i \). The maximum positive integer \( k \) for which a graph \( G \) has a Grundy \( k \)-coloring is the Grundy number \( \Gamma(G) \). Thus, \( 2 \leq \chi(G) \leq \Gamma(G) \leq \psi(G) \) for every nonempty graph \( G \). It is shown that if \( a, b, \) and \( c \) are integers with \( 2 \leq a \leq b \leq c \), then there exists a connected graph \( G \) with \( \chi(G) = a \), \( \Gamma(G) = b \), and \( \psi(G) = c \) if and only if \( a = b = c = 2 \) or \( b \geq 3 \).
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 65-75
- Published: 31/05/2010
Let \( G \) be a simple graph, and let \( p \) be a positive integer. A subset \( D \subseteq V(G) \) is a \( p \)-dominating set of the graph \( G \) if every vertex \( v \in V(G) – D \) is adjacent to at least \( p \) vertices of \( D \). The \( p \)-domination number \( \gamma_p(G) \) is the minimum cardinality among the \( p \)-dominating sets of \( G \). Note that the \( 1 \)-domination number \( \gamma_1(G) \) is the usual domination number \( \gamma(G) \).
A subset \( S \subseteq V(G) \) is said to be a total dominating set if every vertex in \( V(G) \) has at least one neighbor in \( S \), and it is a connected dominating set if the graph induced by \( S \) is connected. The total domination number \( \gamma_t(G) \) represents the cardinality of a minimum total dominating set of \( G \) and the connected domination number \( \gamma_c(G) \) the cardinality of a minimum connected dominating set.
Fink and Jacobson showed in 1985 that if \( G \) is a graph with \( \Delta(G) \geq p \geq 2 \), then \(\gamma_p(G) \geq \gamma(G) + p – 2.\)
In this paper, we will give some sufficient conditions for a graph \( G \) such that \(\gamma_p(G) \geq \gamma(G) + p – 1.\)
We will show that for block graphs \( G \) the inequality \(\gamma_p(G) \geq \gamma_t(G) + p – 2 \) is valid and that for trees \( T \) the inequality \(\gamma_p(T) \geq \gamma_c(T) + p – 1\) holds. Further, we characterize the trees \( T \) with \(\gamma_p(T) = \gamma_c(T) + p – 1,\) \(\gamma_p(T) = \gamma_t(T) + p – 2, \gamma_p(T) = \gamma_t(T) + p – 1,\) and \(\gamma_p(T) = \gamma(T) + p – 1.\)
- Research article
- Full Text
- Journal of Combinatorial Mathematics and Combinatorial Computing
- Volume 073
- Pages: 55-64
- Published: 31/05/2010
Let \( G = (V, E) \) be a connected graph. A dominating set \( S \) of \( G \) is called a neighborhood connected dominating set (\({ncd-set}\)) if the induced subgraph \( \langle N(S) \rangle \) is connected. The minimum cardinality of an ncd-set of \( G \) is called the neighborhood connected domination number of \( G \) and is denoted by \( \gamma_{nc}(G) \). In this paper, we initiate a study of this parameter.




