# Communicators

An MPI communicator specifies the communication context for a communication operation. In particular, it specifies the set of processes which share the context, and assigns each each process a unique rank (see MPI.Comm_rank) taking an integer value in 0:n-1, where n is the number of processes in the communicator (see MPI.Comm_size.

## Types and enums

MPI.ComparisonType
Comparison

An enum denoting the result of Comm_compare:

• MPI.IDENT: the objects are handles for the same object (identical groups and same contexts).

• MPI.CONGRUENT: the underlying groups are identical in constituents and rank order; these communicators differ only by context.

• MPI.SIMILAR: members of both objects are the same but the rank order differs.

• MPI.UNEQUAL: otherwise

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## Constants

MPI.COMM_WORLDConstant
MPI.COMM_WORLD

A communicator containing all processes with which the local rank can communicate at initialization. In a typical "static-process" model, this will be all processes.

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## Functions

### Constructors

MPI.Comm_spawnFunction
Comm_spawn(command, argv::Vector{String}, nprocs::Integer, comm::Comm[, errors::Vector{Cint}]; kwargs...)

MPI.universe_size