QosCosGrid MPI Lab

Prepare your environment

Please read the file located here for instructions.

Materials :

• Cygwin bundle
• Files to configure Emacs (for those of you who are using Linux or Mac OS X, files to add in you ~/.emacs.d/ directory are here and you have to add a few lines to your .emacs file)
• The key

If you have never used MPI, you can find some small examples here.

Now you are ready for the lab

This lab has been prepared with (and mainly by) Éric Rodriguez

• You can get Pierre's presentation here.
• And here is the presentation I made as an introduction [PPT] [SXI].
• MPI web page that provides the standard and some documentation.

We provide you some files in this bundle

• A Makefile ;-)
• debug.c and debug.h are used to do some debug outputs
• ant.h : declaration of the data structures, of some constants, macros...
• ant_tools.c and the corresponding ant_tools.h contain some functions such as the transition rule (that defines how the ants walk around).
• pngant.c contains the functions to write the result as a png picture, so that you can really see the result.

You also have to write some functions in some other provided files

• mpi_tools.c is the file where you write the communication functions.
  • rebuild_solution(struct cell *global_current_cellulae, struct cell *current_cellulae, int my_width) gathers the partial results computed by every process to the process with rank 0.
  • create_data_struct_mpi(void) is used to create two new MPI data structures, called MPI_CELLULAE and MPI_ANT_TRANSFERT.
• ant.c is the main file where the iterations are performed. This is where the main() function is implemented. The function you have to write is the one that manages the boundaries: boundary_treatment(void). We have two issues at the boundaries :
  • When an ant looks around it, it requires a knowledge about the state of the cells nearby. Then each process must send the state of its eastest and westest collumns of cells to its neighbours.
  • Some ants might walk across the boundaries and go from one process to another.

If you need some debug outputs, use the debug(...) function. You just need to include "ant.h" in you file (in the files we provide you, it is already included), and use it as printf. The only difference is that you don't have to add \n at the end of your output, debug(..) does it for you.

We propose a solution here.