- Tytuł:
- Balancedness and the Least Laplacian Eigenvalue of Some Complex Unit Gain Graphs
- Autorzy:
-
Belardo, Francesco
Brunetti, Maurizio
Reff, Nathan - Powiązania:
- https://bibliotekanauki.pl/articles/31540652.pdf
- Data publikacji:
- 2020-05-01
- Wydawca:
- Uniwersytet Zielonogórski. Wydział Matematyki, Informatyki i Ekonometrii
- Tematy:
-
gain graph
Laplacian eigenvalues
balanced graph
algebraic frustration - Opis:
- Let \(\mathbb{T}_4 = {±1, ±i}\) be the subgroup of 4-th roots of unity inside \(\mathbb{T}\), the multiplicative group of complex units. A complex unit gain graph \(\Phi\) is a simple graph $Γ = (V(Γ) = {v_1, . . ., v_n}, E(Γ))$ equipped with a map \(\varphi:\overrightarrow{E}(Γ)→\mathbb{T}\) defined on the set of oriented edges such that \(\varphi(v_iv_j) = \varphi(v_jv_i)^{−1}\). The gain graph \(\Phi\) is said to be balanced if for every cycle $C = v_{i_1}v_{i_2} . . . v_{i_k}v_{i_1}$ we have \(\varphi(v_{i_1}v_{i_2})\varphi(v_{i_2}v_{i_3}) . . . \varphi(v_{i_k}v_{i_1}) = 1\). It is known that \(\Phi\) is balanced if and only if the least Laplacian eigenvalue \(\lambda_n(\Phi)\) is 0. Here we show that, if \(\Phi\) is unbalanced and \(\varphi(\Phi) ⊆ \mathbb{T}_4\), the eigenvalue \(\lambda_n(\Phi)\) measures how far is \(\Phi\) from being balanced. More precisely, let \(ν(\Phi)\) (respectively, \(∈(\Phi)\)) be the number of vertices (respectively, edges) to cancel in order to get a balanced gain subgraph. We show that \(\lambda_n(\Phi) ≤ ν(\Phi) ≤ ∈(\Phi)\). We also analyze the case when \(\lambda_n(\Phi) = ν(\Phi)\). In fact, we identify the structural conditions on \(\Phi\) that lead to such equality.
- Źródło:
-
Discussiones Mathematicae Graph Theory; 2020, 40, 2; 417-433
2083-5892 - Pojawia się w:
- Discussiones Mathematicae Graph Theory
- Dostawca treści:
- Biblioteka Nauki
Artykuł