In the mathematical discipline of graph theory, a subset of vertices in a graph G is called dissociation if it induces a subgraph with maximum degree 1. The number of vertices in a maximum cardinality dissociation set in G is called the dissociation number of G, denoted by diss(G). The problem of computing diss(G) (dissociation number problem) was firstly studied by Yannakakis.^[1][2] The problem is NP-hard even in the class of bipartite and planar graphs.^[3]

An algorithm for computing a 4/3-approximation of the dissociation number in bipartite graphs was published in 2022.^[4]

The dissociation number is a special case of the more general Maximum k-dependent Set Problem for ${\displaystyle k=1}$. The problem asks for the size of a largest subset ${\displaystyle S}$ of the vertices of a graph ${\displaystyle G}$, so that the induced subgraph ${\displaystyle G[S]}$ has maximum degree ${\displaystyle k}$.