  Computing modular coincidences can show whether a given substitution system,
which is supported on a point lattice in R^d, consists of model sets or not. We
prove the computatibility of this problem and determine an upper bound for the
number of iterations needed. The main tool is a simple algorithm for computing
modular coincidences, which is essentially a generalization of Dekking
coincidence to more than one dimension, and the proof of equivalence of this
generalized Dekking coincidence and modular coincidence. As a consequence, we
also obtain some conditions for the existence of modular coincidences. In a
separate section, and throughout the article, a number of examples are given.
