Type Matching

Recall that a MPI derived datatype has the form

{(t_0,d_0),(t_1,d_1),…,(t_n-1,d_n-1)}

(t_0,t_1,…,t_n-1) is called the type signature

The fundamental rule for type matching in MPI is that the type

signatures specified by the sender and receiver must be compatible

Let the type signature of the recv be (u_0,u_1,…,u_m) and of the

send be (t_0,t_1,…,t_n-1)

Then the type signatures are compatible if

m>=n and t_0=u_0, t_1=u_1,…,t_n=u_n

Note that if count is greater than 1 the type signature is obtained by

concatenating count copies of the datatype

Caveat: for collective communications the type signatures specified but

the processes in the collective must be identical

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