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What is the difference between ranks and processes in MPI?
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MPI process rank Each process has a unique rank, i.e. an integer identifier, within a. communicator. The rank value is between 0 and #procs-1. The rank value is used to distinguish one process from another. Commands MPI Comm size & MPI Comm rank are very useful.
The Message Passing Interface (MPI) is an Application Program Interface that defines a model of parallel computing where each parallel process has its own local memory, and data must be explicitly shared by passing messages between processes.
Broadcasting with MPI_Bcast During a broadcast, one process sends the same data to all processes in a communicator. One of the main uses of broadcasting is to send out user input to a parallel program, or send out configuration parameters to all processes.
It was developed by OPHI with the United Nations Development Programme (UNDP) in 2010. It is a part of UNDP's Human Development Report (HDR) and is released annually. MPI 2021 was released in September 2021. India ranked 62 in the Global MPI 2020 which ranked 107 countries.
Here is the resource I learned all my MPI from, you might find it useful.
As to your question: processes are the actual instances of the program that are running. MPI allows you to create logical groups of processes, and in each group, a process is identified by its rank. This is an integer in the range [0, N-1] where N is the size of the group. Communicators are objects that handle communication between processes. An intra-communicator handles processes within a single group, while an inter-communicator handles communication between two distinct groups.
By default, you have a single group that contains all your processes, and the intra-communicator MPI_COMM_WORLD that handles communication between them. This is sufficient for most applications, and does blur the distinction between process and rank a bit. The main thing to remember is that the rank of a process is always relative to a group. If you were to split your processes into two groups (e.g. one group to read input and another group to process data), then each process would now have two ranks: the one it originally had in MPI_COMM_WORLD, and one in its new group.
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