Telephone with MPI

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In this HW, we will cover some Message Passing Interface (MPI) basics. If you have any questions, don't hesitate to post on Ed or come to OH!

Submission: A tarball/git-link of the provided directory

The Game of Telephone, with Children

In the children's game of telephone, n children gather clockwise in a circle, numbered 0 through n-1. Child 0, known as the caller, whispers a message to Child 1 on the right. The message continually passes to Child 2, Child 3... Child n-1, and then back to Child 0. As children do not enunciate their words properly (and some may be naughty), the caller's original message is often garbled up into something completely different.

The Game of Telephone, with MPI

We want you to implement telephone in MPI. Start with n MPI ranks and a distinguished string. MPI rank 0 sends the string to MPI rank 1, MPI rank 1 then sends string to MPI Rank 2... so on and so forth until the string goes back to MPI rank 0. Before each rank transmits its string, a function garble() is applied to the string. We have provided a skeleton code telephone.c to be used in the following way:

Let's start with an example:

mpirun -n 3 ./telephone "Testing"

The first argument (3) denotes the number of MPI ranks and the second argument ("Testing") denotes the string to be passed around. The output should be the following:

MPI rank 0 starting message: "Testing"
MPI rank 1 recieved message: "Teshing"
MPI rank 2 recieved message: "Meshing"
MPI rank 0 recieved message: "Mashing"

There are three MPI ranks. Rank 0 starts with the original string, and each time the message moves to a different rank it changes due to garble(). You should not need any other MPI functions besides MPI_Send() and MPI_Recv()

More generally, telephone should be used in the following way:

mpirun -n NumRanks ./telephone String

We have provided a makefile and a submission script. For submission, please take a look at telephone.c and finish the telephone implementation.

Concluding Thoughts

If you are still having trouble, please see the basic Ping Pong program in this link. It is quite similar to our game of Telephone, so reading it will provide a few hints and tips!