Abstract. Let R = ⊕ i∈ޚ R i be a −ޚgraded ring and M = ⊕ i∈ޚ M i be a graded R-module. Providing some results on graded multiplication modules, some equivalent conditions for which a finitely generated graded R-module to be graded multiplication will be given. We define generalised graded multiplication module and determine some of its certain graded prime submodules. It will be shown that any graded submodule of a finitely generated generalised graded multiplication R-module M has a kind of primary decomposition. Using this, we give a characterisation of graded primary submodules of M. These lead to a kind of characterisation of finitely generated generalised graded multiplication modules.2010 Mathematics Subject Classification. 13A02, 13C05, 13C13, 13C99.
Introduction.Let R be a commutative ring with a non-zero identity and M be a unital R-module. Then M is called a multiplication module if any submodule N of M has the form aM for some ideal a of R [4]. This gives N = aM = (N : R M)M, where (N : R M) = {r ∈ R : rM ⊆ N} is the residual of N by M. The ring R is called a multiplication ring if any ideal of R is a multiplication R-module in the above sense [12]. These concepts have attracted the interest of several authors in the last two decades, and have led to more information on the structure of R-modules (see for example [2, 3, 7, 20, 21]). In [9], multiplication modules in the category of R-modules graded by a group G were introduced and some interesting results were obtained (see also [8]). Nevertheless, based on the author's knowledge few results are known on this concept. In this paper we deal with the category of graded multiplication modules over a -ޚgraded ring R and obtain some concerning results. More precisely, among other things, it will be shown that for a graded submodule N of a finitely generated generalised graded multiplication R-module M, there exists a primary decomposition N = p∈P N(p), where P denotes the set of all minimal primes of (N : R M). We also show that for a finitely generated graded multiplication R-module M, this kind of primary decomposition for each submodule N of M, together with other two conditions, gives that M must be a generalised graded multiplication R-module. It should be noted that all of the results remain valid if one replaces the grading group ޚ with any torsion-free abelian group G having a total order compatible with its structure. However, for the convenience we are interested in more concrete abelian group .ޚ The organisation of the paper is as follows. In Section 2, we collect some preliminary results on graded multiplication modules. Some characterisations for