Agenda

• Announcements
• Homework/Lab 4
• MPI
• Sample Applications
  • Conway's Game of Life
  • Computing the Mandelbrot set

Announcements

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Message Passing Interface (MPI)

The first part of the notes on MPI are available in Lecture 7.

MPI - Collective Communication functions

mpicoll.tgz Also available in /home/faculty/terescoj/shared/cs338/lect08.

• MPI_Barrier(MPI_Comm comm) - synchronize procs
• MPI_Bcast(void *buf,int count,MPI_Datatype type,int root,MPI_Comm comm) - broadcast - sends count copies of data of type type located in buf on proc root to buf on all others.
• MPI_Reduce(void *sendbuf,void *recvbuf,int count,
  MPI_Datatype type,MPI_Op op,int root,MPI_Comm comm) - combines data in sendbuf on each proc using operation op and stores the result in recvbuf on proc root
• MPI_Allreduce() - same as reduce except result is stored in recvbuf on all procs.
• MPI_Op values - MPI_MAX, MPI_MIN, MPI_SUM, MPI_PROD, MPI_LAND, MPI_BAND, MPI_LOR, MPI_BOR, MPI_LXOR, MPI_BXOR, MPI_MAXLOC, MPI_MINLOC plus user-defined.
• MPI_Scan(void *sendbuf,void *recvbuf,int count,MPI_Datatype type,MPI_Op op,MPI_Comm comm) - parallel prefix scan operations

MPI - Scatter/Gather

mpiscatgath.tgz Also available in /home/faculty/terescoj/shared/cs338/lect08.

• MPI_Scatter(void *sendbuf,int sendcount,MPI_Datatype sendtype,void *recvbuf,int recvcount,MPI_Datatype
  recvtype,int root,MPI_Comm comm) - root sends sendcount items from sendbuf to each processor. Each processor receives recvcount items into recvbuf
• MPI_Gather(void *sendbuf,int sendcount,MPI_Datatype sendtype,void *recvbuf,int recvcount,MPI_Datatype
  recvtype,int root,MPI_Comm comm) - each proc sends sendcount items from sendbuf to root. root receives recvcount items into recvbuf from each proc
• MPI_Scatterv/MPI_Gatherv work with variable-sized chunks of data
• MPI_Allgather/MPI_Alltoall variations of scatter/gather

To understand what is going on with the various broadcast and scatter/gather functions, consider this figure, taken from the MPI Standard, p.91

Sample Applications

Conway's Game of Life

The Game of Life was invented by John Conway in 1970. The game is played on a field of cells, each of which has eigh neighbors (adjacent cells). A cell is either occupied (by an organism) or not. The rules for deriving a generation from the previous one are:

• Death: If an occupied cell has 0, 1, 4, 5, 6, 7, or 8 occupied neighbors, it dies (of either boredom or overcrowding, as the case may be)
• Survival: If an occupied cell has 2 or 3 occupied neighbors, it survives to the next generation
• Birth: If an unoccupied cell has 3 occupied neighbors, it becomes occupied.

The game is very interesting in that complex patterns and cycles arise. Do a google search to find plenty of Java applets you can try out.

Serial version: life.tgz Also available in /home/faculty/terescoj/shared/cs338/lect08.

MPI version: mpilife.tgz Also available in /home/faculty/terescoj/shared/cs338/lect08.

Computing the Mandelbrot Set

Some Mandelbrot Set Information and pictures

Java Threads version: mand-java.tgz Also available in /home/faculty/terescoj/shared/cs338/lect08.

MPI version: mand-mpi.tgz Also available in /home/faculty/terescoj/shared/cs338/lect08.