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Questions and Answers
What is the primary purpose of the MPI_Send function?
What is the primary purpose of the MPI_Send function?
- To send a message to another process (correct)
- To receive a message from another process
- To initialize the MPI environment
- To manage the MPI processes
What information does the MPI_Status object provide?
What information does the MPI_Status object provide?
- The source process, message tag, and error status (correct)
- The message buffer and datatype
- Only the message tag
- Only the source process of the message
What is the purpose of the MPI_Get_count function?
What is the purpose of the MPI_Get_count function?
- To get the number of received elements (correct)
- To get the datatype of the message
- To get the source process of the message
- To get the message tag
What is the main benefit of using non-blocking communication functions?
What is the main benefit of using non-blocking communication functions?
What is the recommended approach when using MPI communication functions?
What is the recommended approach when using MPI communication functions?
What is the responsibility of the programmer when using non-blocking communication functions?
What is the responsibility of the programmer when using non-blocking communication functions?
What is the primary function of MPI_Init?
What is the primary function of MPI_Init?
Which MPI function is used to get the size of a communicator?
Which MPI function is used to get the size of a communicator?
What is characteristic of blocking communication functions in MPI?
What is characteristic of blocking communication functions in MPI?
What is the purpose of MPI_Finalize?
What is the purpose of MPI_Finalize?
Which MPI function is used to send a message to another process?
Which MPI function is used to send a message to another process?
What is the function of MPI_Comm_rank?
What is the function of MPI_Comm_rank?
What is the purpose of the MPI_Bcast function?
What is the purpose of the MPI_Bcast function?
What is the difference between MPI_Scatter and MPI_Gather?
What is the difference between MPI_Scatter and MPI_Gather?
What is the purpose of the MPI_Irecv function?
What is the purpose of the MPI_Irecv function?
What is the main use of broadcasting in MPI?
What is the main use of broadcasting in MPI?
What is the difference between MPI_Alltoall and MPI_Alltoallv?
What is the difference between MPI_Alltoall and MPI_Alltoallv?
What is the purpose of the MPI_Isend function?
What is the purpose of the MPI_Isend function?
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Study Notes
MPI Core Functions
- MPI_Init: initializes the MPI library, must be the first routine called
- MPI_Comm_size: gets the size of a communicator
- MPI_Comm_rank: gets the rank of the calling process in the communicator
- MPI_Send: sends a message to another process
- MPI_Recv: receives a message from another process
- MPI_Finalize: cleans up all MPI state, must be the last MPI function called by a process
MPI Communication Functions
- Two types: Blocking Communication Functions and Non-blocking Communication Functions
Blocking Communication Functions
- MPI_Send: sends a message to another process, data must be successfully sent or safely copied to system buffer space
- MPI_Recv: receives a message from another process, data must be safely stored in the receive buffer
Non-blocking Communication Functions
- MPI_Isend: non-blocking send, returns without waiting for the communication to complete
- MPI_Irecv: non-blocking receive, returns without waiting for the communication to complete
MPI Collective Communication
- MPI_Bcast: broadcasts a message from the process with rank "root" to all other processes in the group
- MPI_Scatter: splits the message into n equal segments, with the ith segment sent to the ith process in the group
- MPI_Gather: collects a total of n data items from all other processes in the group at a single process
- MPI_Alltoall: all-to-all communication, where every process sends and receives n data segments
- MPI_Alltoallv: customizable all-to-all communication, where each process sends/receives a customizable amount of data to/from each process
Status Object
- Used after completion of a receive to find the actual length, source, and tag of a message
- Provides information about:
- Source process for the message (status.MPI_SOURCE)
- Message tag (status.MPI_TAG)
- Error status (status.MPI_ERROR)
- The number of elements received is given by: MPI_Get_count(MPI_Status *status, MPI_Datatype datatype, int *count)
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