Examples Using Other Languages

3 – Using InfiniPath MPI Getting Started with MPI

Here ./cpi designates the executable of the example program in the working directory. The -npparameter to mpirun defines the number of processes to be used in the parallel computation. Now try it with four processes:

$ mpirun -np 4 -m mpihosts ./cpi Process 3 on hostname1 Process 0 on hostname2 Process 2 on hostname2 Process 1 on hostname1

pi is approximately 3.1416009869231249, Error is 0.0000083333333318

wall clock time = 0.000603

If you run the program several times with the same value of the -npparameter, you may get the output lines in different orders. This is because they are issued by independent asynchronous processes, so their order is non-deterministic.

The number of processes can be greater than the number of nodes. In this four-process example, the mpihosts file listed only two hosts, hostname1 and hostname2. Generally, mpirun will try to distribute the specified number of processes evenly among the nodes listed in the mpihosts file, but if the number of processes exceeds the number of nodes listed in the mpihosts file, then some nodes will be assigned more than one instance of the program.

Up to a limit, the number of processes can even exceed the total number of processors on the specified set of nodes, although it is usually detrimental to performance to have more than one node program per processor. This limit is eight processes per node with the QHT7140, and four processes per node with the QLE7140. See section 3.5.9 for further discussion.

Details on alternate means of specifying the mpihosts file are given in section 3.5.6. Further information on the mpirun options are in section 3.5.5, section 3.5.9 and section 3.5.10.

3.3.2

This section gives more examples, one for Fortran77, one for Fortran90, and one for C++. Fortran95 usage will be similar to that for Fortran90.

fpi.f is a Fortran77 program that computes pi in a way similar to cpi.c. Compile and link it with:

$ mpif77 -o fpi3 fpi3.f

and run it with:

$ mpirun -np 2 -m mpihosts ./fpi3

pi3f90.f90 in the same directory is a Fortran90 program that does essentially the same computation. Compile and link it with:

$ mpif90 -o pi3f90 pi3f90.f90

IB6054601-00 D

3-3

IB6054601-00 D specifications

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Q-Logic IB6054601-00 D manual Examples Using Other Languages, Run it with, $ mpif77 -o fpi3 fpi3.f

Models: IB6054601-00 D