Abstract
A signed graph $(G,sigma)$ is a graphâ âtogether with an assignment of signs ${+,-}$ to its edges whereâ â$sigma$ is the subset of its negative edgesâ. âThere are a few variants of coloring and clique problems ofâ âsigned graphsâ, âwhich have been studiedâ. âAn initial version known as vertex coloring of signed graphs is defined by Zaslavsky in $1982$â. âRecently Naserasr et. al., in [Râ. âNaserasrâ, âEâ. âRollova and Eâ. âSopenaâ, âHomomorphisms of signed graphsâ, âJâ. âGraph Theoryâ, 79ââ (2015) 178--212, have defined signed chromatic and signed clique numbers of signed graphsâ. âIn this paper we consider the latter mentioned problems for signed interval graphsâ. âWe prove that the coloring problem of signedâ âinterval graphs is NP-complete whereas their ordinary coloringâ âproblem (the coloring problem of interval graphs) is in Pâ. âMoreover we prove that the signed clique problem of aâ âsigned interval graph can be solved in polynomial timeâ. âWe also consider theâ âcomplexity of further related problemsâ.
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