Published online by Cambridge University Press: 20 November 2018
A Mauldin–Williams graph   $M$  is a generalization of an iterated function system by a directed graph. Its invariant set
 $M$  is a generalization of an iterated function system by a directed graph. Its invariant set   $K$  plays the role of the self-similar set. We associate a
 $K$  plays the role of the self-similar set. We associate a   ${{C}^{*}}$ -algebra
 ${{C}^{*}}$ -algebra   ${{O}_{M}}\left( K \right)$  with a Mauldin–Williams graph
 ${{O}_{M}}\left( K \right)$  with a Mauldin–Williams graph   $M$  and the invariant set
 $M$  and the invariant set   $K$ , laying emphasis on the singular points. We assume that the underlying graph
 $K$ , laying emphasis on the singular points. We assume that the underlying graph   $G$  has no sinks and no sources. If
 $G$  has no sinks and no sources. If   $M$  satisfies the open set condition in
 $M$  satisfies the open set condition in   $K$ , and
 $K$ , and   $G$  is irreducible and is not a cyclic permutation, then the associated
 $G$  is irreducible and is not a cyclic permutation, then the associated   ${{C}^{*}}$ -algebra
 ${{C}^{*}}$ -algebra   ${{O}_{M}}\left( K \right)$  is simple and purely infinite. We calculate the
 ${{O}_{M}}\left( K \right)$  is simple and purely infinite. We calculate the   $K$ -groups for some examples including the inflation rule of the Penrose tilings.
 $K$ -groups for some examples including the inflation rule of the Penrose tilings.