CODEWITHSUNDEEP
mpi
DonJoe
DonJoe

Reputation: 1763

Does Mpi Scatter send data in any kind of order

I saw this on internet

MPI_Scatter takes an array of elements and distributes the elements in the order of process rank.

But I could not find it on the documentation.

I have an array and there are 4 processes. One process is root -> will scatter data among other 3 processes. The id-s are 0, 1, 2, 3.

Question: Will MPI_Scatter() or MPI_Scatterv() send the data in order, guaranteed?

Example 1: 

0: [a, b, c, d, e]

// after scatter

1: [a, b]
2: [c, d]
3: [e]

Example 2:

0: [a, b]

// after scatter

1: [a]
2: [b]
3: [ ]

Also, does gather do the same thing? (preserve order)

Upvotes: 0

Views: 2306

Answers (1)

itsnevertoobadtoaskforhelp
itsnevertoobadtoaskforhelp

Reputation: 316

The order is guaranteed according to the rank in the MPI_Comm.

Below statement is copy pasted from open-mpi v2.1 documentation:

An alternative description is that the root sends a message with MPI_Send(sendbuf, sendcount * n, sendtype, ...). This message is split into n equal segments, the ith segment is sent to the ith process in the group, and each process receives this message as above. The send buffer is ignored for all nonroot processes.

Upvotes: 2

Related Questions