PROGRAM HW1 
!
! Program for performing code and compiler optimization experiments.
! Author: Ming Xue, 2003. Modified 2005.
!
  IMPLICIT NONE
  INTEGER :: n
  PARAMETER(n=5000)
  REAL :: a(n,n),b(n,n),c(n,n),d(n,n),e(n,n),f(n,n)
  REAL :: t1,t2,cputime
  REAL :: tmp(2)
  REAL :: etime

  INTEGER :: i,j

  a = 1.0
  b = 2.0
  c = 2.0
  d = 4.0
  e = 5.0
  f = 6.0
 
!------------------------------------------------------------------------------
! Section 1a
!------------------------------------------------------------------------------
 
  t1 = etime(tmp)
  DO i = 1,n
    DO j = 1,n
      a(i,j) = (a(i,j)*b(i,j) + c(i,j)*d(i,j))**0.315
    ENDDO
  ENDDO

  t2 = etime(tmp)
  PRINT *, 'CPU time used by section 1a  was ', t2 - t1,'(s)'

!------------------------------------------------------------------------------
! Section 1b
!------------------------------------------------------------------------------

  t1 = etime(tmp)
  DO j = 1,n
    DO i = 1,n
      a(i,j) = (a(i,j)*b(i,j) + c(i,j)*d(i,j))**0.315
    ENDDO
  ENDDO

  t2 = etime(tmp)
  PRINT *, 'CPU time used by section 1b was ', t2 - t1,'(s)'


!------------------------------------------------------------------------------
! Section 1c
!------------------------------------------------------------------------------

  t1 = etime(tmp)
  DO j = 1,n
    DO i = 1,n
      e(i,j) = a(i,j)*b(i,j)
    ENDDO
  ENDDO

  DO j = 1,n
    DO i = 1,n
      f(i,j) = c(i,j)*d(i,j)
    ENDDO
  ENDDO

  DO j = 1,n
    DO i = 1,n
      a(i,j) = (e(i,j) + f(i,j))**0.315
    ENDDO
  ENDDO

  t2 = etime(tmp)
  PRINT *, 'CPU time used by section 1c  was ', t2 - t1,'(s)'


!------------------------------------------------------------------------------
! Section 1d - array syntax array operations
!------------------------------------------------------------------------------

  t1 = etime(tmp)

  a = (a * b + c * d )**0.315

  t2 = etime(tmp)
  PRINT *, 'CPU time used by section 1d was ', t2 - t1,'(s)'

!------------------------------------------------------------------------------
! Section 1e
!------------------------------------------------------------------------------

  t1 = etime(tmp)

  DO j = 1,n
    DO i = 2,n
      a(i,j) = (a(i-1,j)*b(i,j) + c(i,j)*d(i,j))**0.315
    ENDDO
  ENDDO

  t2 = etime(tmp)
  PRINT *, 'CPU time used by section 1e was ', t2 - t1,'(s)'

!------------------------------------------------------------------------------
! Section 2a
!------------------------------------------------------------------------------

  t1 = etime(tmp)

  DO j =1,n
    DO i= 1,n
      CALL SUB1(a(i,j), b(i,j), c(i,j), d(i,j),i,j)
    END DO
  END DO

  t2 = etime(tmp)

  PRINT *, 'CPU time used by section 2a was ', t2 - t1,'(s)'

!------------------------------------------------------------------------------
! Section 2b
!------------------------------------------------------------------------------

  t1 = etime(tmp)

  CALL SUB2(a,b,c,d,n)

  t2 = etime(tmp)

  PRINT *, 'CPU time used by section 2b was ', t2 - t1,'(s)'

  STOP
END PROGRAM HW1 

SUBROUTINE SUB1 (a,b,c,d,i,j)
  IMPLICIT NONE
  REAL :: a,b,c,d
  INTEGER :: i,j
  a =  (a*b + c*d)**0.315
  RETURN
END SUBROUTINE SUB1

SUBROUTINE SUB2(a,b,c,d,n)
  IMPLICIT NONE
  INTEGER :: n
  REAL :: a(n,n),b(n,n),c(n,n),d(n,n)
  INTEGER :: i,j
  REAL :: t1,t2,cputime
  REAL :: tmp(2)
  REAL :: etime

  t1 = etime(tmp)

  DO j =1,n
    DO i= 1,n
      a(i,j)=  (a(i,j)*b(i,j) + c(i,j)*d(i,j))**0.315
    END DO
  END DO

  t2 = etime(tmp)
  PRINT *, 'CPU time used by section 2b inside sub2 was ', t2 - t1,'(s)'

  RETURN
END SUBROUTINE SUB2 

REAL FUNCTION cputime()
  cputime = mclock()/100.
  RETURN
END FUNCTION cputime

REAL FUNCTION f_cputime()
  REAL :: tmp(2)

!------------------------------------------------------------------------------
! SUN/DEC/SGI  DEFINITION FOR TIMING
!------------------------------------------------------------------------------

  f_cputime = etime(tmp)

  RETURN
END FUNCTION f_cputime