On the Edge Decomposition of the Complete Multipartite Graph and Certain Generalized Petersen Graphs into Locally Irregular Subgraphs
DOI:
https://doi.org/10.11113/mjfas.v21n6.4250Keywords:
Locally irregular, subcubic graph, complete multipartite graph, generalized Petersen graphAbstract
The least number of colors to decompose a graph into a locally irregular edge coloring is the locally irregular chromatic index and is denoted by <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>χ</mi><mo>'</mo><mstyle mathvariant="normal"><mtext>irr</mtext></mstyle><mo>(</mo><mi>G</mi><mo>)</mo></math>. In 2015, Baudon et al. showed that, for the complete bipartite graph <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>K</mi><mi>m,n</mi></msub></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>χ</mi><mo>'</mo><mstyle mathvariant="normal"><mtext>irr</mtext></mstyle><mo>(</mo><msub><mi>K</mi><mi>m,n</mi></msub><mo>)</mo><mo>=</mo><mn>3</mn></math>.
In this paper, we determine the locally irregular chromatic index for complete multipartite graphs. In 2023, B. Lužar et al. conjectured that, for generalized Petersen graphs <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo></math> with girth at least 5 (except <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mn>5</mn><mo>,</mo><mn>2</mn><mo>)</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mn>7</mn><mo>,</mo><mn>2</mn><mo>)</mo></math>), <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>χ</mi><mo>'</mo><mstyle mathvariant="normal"><mtext>irr</mtext></mstyle><mo>(</mo><mi>GP</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo><mo>)</mo><mo>=</mo><mn>3</mn></math>.
Here, we partially verify the conjecture for <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mi>n</mi><mo>,</mo><mn>2</mn><mo>)</mo></math> and determine the exact values for <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mn>5</mn><mo>,</mo><mn>2</mn><mo>)</mo></math>, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mn>7</mn><mo>,</mo><mn>2</mn><mo>)</mo></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>GP</mi><mo>(</mo><mn>9</mn><mo>,</mo><mn>2</mn><mo>)</mo></math>. The exact values of <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>χ</mi><mo>'</mo><mstyle mathvariant="normal"><mtext>irr</mtext></mstyle><mo>(</mo><mi>GP</mi><mo>(</mo><mi>n</mi><mo>,</mo><mi>k</mi><mo>)</mo><mo>)</mo></math> are also determined for cases when <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>n</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>k</mi></math> satisfy certain conditions.
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