This topic describes MPI's global computation routines: reduce and scan.

In MPI, there are two types of global computation routines: reduce and scan. These routines output the full and incremental results, respectively, of applying an operation to a distributed data array. The global operation to be performed is passed to the routine as an argument identifying a function, which can be either a predefined MPI function or a user-supplied function.

MPI provides four global computation routines in total. In this topic, we start by discussing the three varieties of reduction computation. We then discuss scan computation.