1) Set the maximum number of threads to 12 using environmental
variables.

Answer:

setenv OMP_NUM_THREADS 12



2) Make an OpenMP program that

   a) prints the maximum number of threads available,
   b) set the number of threads to 8,
   c) prints 'Hello, I am thread [thread number]' from every thread.

Answer:

PROGRAM OMP_PROG
  USE omp_lib
  IMPLICIT NONE

  INTEGER :: TID,OMP_GET_MAX_THREADS,OMP_GET_THREAD_NUM

  TID = OMP_GET_MAX_THREADS()
  PRINT *, 'max thread = ', TID

  CALL omp_set_num_threads(8)

!$OMP PARALLEL PRIVATE(TID)

  TID = OMP_GET_THREAD_NUM()
  PRINT *, 'Hello from thread = ', TID
!$OMP END PARALLEL

END PROGRAM OMP_PROG



3) Make a simple vector-add program (C(I)=A(I)+B(I) for all
I=1,...,N), where

   * Arrays A, B, C, and variable N will be shared by all threads.
   * Variable I will be private to each thread; each thread will have
     its own unique copy.
   * The iterations of the loop will be distributed dynamically in
     CHUNK sized pieces.
   * Threads will not synchronize upon completing their individual
     pieces of work.

Answer:

      PROGRAM VEC_ADD_DO

      INTEGER N, CHUNKSIZE, CHUNK, I
      PARAMETER (N=1000) 
      PARAMETER (CHUNKSIZE=100) 
      REAL A(N), B(N), C(N)

!     Some initializations
      DO I = 1, N
        A(I) = I * 1.0
        B(I) = A(I)
      ENDDO
      CHUNK = CHUNKSIZE
        
!$OMP PARALLEL SHARED(A,B,C,CHUNK) PRIVATE(I)

!$OMP DO SCHEDULE(DYNAMIC,CHUNK)
      DO I = 1, N
         C(I) = A(I) + B(I)
      ENDDO
!$OMP END DO NOWAIT

!$OMP END PARALLEL

      END



4) Try to utilize OpenMP in your own program.