HP-MPI User's Guide (11th Edition)

Example applications

compute_pi.f

Appendix A 241

compute_pi.f

This Fortran 77 example computes pi by integrating f(x) = 4/(1 + x

Each process:

• Receives the number of intervals used in the approximation

• Calculates the areas of its rectangles

• Synchronizes for a global summation

Process 0 prints the result of the calculation.

program main

include 'mpif.h'

double precision PI25DT

parameter(PI25DT = 3.141592653589793238462643d0)

double precision mypi, pi, h, sum, x, f, a

integer n, myid, numprocs, i, ierr

C Function to integrate

f(a) = 4.d0 / (1.d0 + a*a)

call MPI_INIT(ierr)

call MPI_COMM_RANK(MPI_COMM_WORLD, myid, ierr)

call MPI_COMM_SIZE(MPI_COMM_WORLD, numprocs, ierr)

print *, "Process ", myid, " of ", numprocs, " is alive"

sizetype = 1

sumtype = 2

if (myid .eq. 0) then

n = 100

endif

call MPI_BCAST(n, 1, MPI_INTEGER, 0, MPI_COMM_WORLD, ierr)

C Calculate the interval size.

h = 1.0d0 / n

sum = 0.0d0

do 20 i = myid + 1, n, numprocs

x = h * (dble(i) - 0.5d0)

sum = sum + f(x)

20 continue

mypi = h * sum