C*********************************************************************
c
c		C-DAC Tech Workshop : hyPACK-2013
c                           October 15-18, 2013
c
C Example 3.3           : omp-maxof-elements-reductionop.f  
C
C Objective             : Write an OpenMP program to print Largest element of
C               	  an array.
C               	  This example demonstrates the use of
C               	  OMP_PARALLEL DO loop and REDUCTION operation
C 
C Input                 : Number of elements of an array
C               	  User has to set OMP_NUM_THREADS environment variable for
C               	  n number of threads.
C
C Output                : Each thread checks with its available iterations and
C               	  finally master thread prints the maximum value in the array
C                                                                        
c Created               : August-2013
c
c E-mail                : hpcfte@cdac.in     
c
C************************************************************************

       program MaxOfElements
       integer SIZE
       parameter (SIZE=100000)
       real Array(SIZE), LargeNumber, MaxNumber

       integer OMP_GET_THREAD_NUM, ThreadID
       integer NoofElements 
       integer Seed, iseed

       real MaxOfNumber, CheckValue

       print*,"Enter the number of elements"
       read(*,*) NoofElements

       if((NoofElements .le. 0) .or. (NoofElements .gt. SIZE)) then
          print*,"Input is Wrong."
          print*,"Please try with another number less than",SIZE+1
          print*,"Or greater than 0"
          goto 100
       endif

        call surand(Seed, Size, NoofElements,Array)
c       Seed = 80629.0
c       call surand(Seed, NoofElements, Array)
c       do i = 1, NoofElements
c          print*,"Array(",i,")=",Array(i)
c       enddo

C$OMP PARALLEL DO REDUCTION(MAX:LargeNumber)
       do j = 1, NoofElements
         LargeNumber = MaxOfNumber(Array(j), LargeNumber)
       enddo
C$OMP END PARALLEL DO

       MaxNumber = LargeNumber

       CheckValue = Array(1)
       do i = 2, Noofelements
          if (Array(i) .gt. CheckValue) then
             CheckValue = Array(i)
          endif
       enddo

       if (CheckValue .eq. MaxNumber) then
          print*,"The Maximum value is same using serial computation"
          print*,"and openmp directive"
       else
         print*,"The Maximum value is not same using serial computation"
          print*,"and openmp directive"
       endif

       print*,"The largest number in the array is", MaxNumber

100    end


C This function returns the maximum of two numbers.

       real function MaxOfNumber(ArrayElement, Number)
       real ArrayElement
       real Number
      if(ArrayElement .gt. Number) then
          Number = ArrayElement
       endif

       MaxOfNumber = Number
       return
       end
c
c     **********************************************************
      subroutine surand(Seed, SIZE, NoofElements,Array)
c     *********************************************************
c
      integer iseed
      integer SIZE
      real Array(SIZE)

      do i = 1, NoofElements
          iseed = (i+1) * Seed
          Array(i) = ran(iseed)
          write(6,150) i, Array(i);
150       format(5x, i8, f16.7)
       enddo
      return
      end
c     *******************************************************