program ArrayExample
! This file:
! http://ftp.aset.psu.edu/pub/ger/fortran/hdk/ArrayExample.f90

  integer :: i
  integer, parameter:: n1=3, n2=4
  real :: a, b
  dimension :: b(n1), a(n1,n2)
  a = 2.5; ! The means shoud all be 2.5.

!Question from: Roland posted on comp.lang.fortran on 11 September 2006:
!I have a 2-D array, a(n1, n2), and I want to compute the mean of each
!row of the array and save the values in array b(n1). To accomplish this
!task, I could write in Fortran 90

  do i=1, n1
      b(i)=sum(a(i, :))/n2
  enddo
  print *, "b=",b

!which needs three (3) lines of coding.
!Now my question: Is there a way in Fortran 90 to put the above three
!lines into just one (1) line?
!
!
!Richard Maine's Reply:
!See the DIM= argument to SUM. That's exactly the kind of thing it is
!for.

  b = sum(a,dim=2)/n2
  print *, "b=",b


!Brooks Moses Reply:
  b = (/ (sum(a(i,:))/n2, i=1, n1) /)
  print *, "b=",b

!or

  forall(i=1:n1) b(i)=sum(a(i,:))/n2
  print *, "b=",b


!Glen Hemannsfeldt and then Jaroslav Highegg Reply
! (more than one line, but perhaps more optimizable?):
  b = 0
  do j=1,n2
    b = b + a(:,j)
  end do
  b = b/n2
  print *, "b=",b


!Simon Geard Reply:
!
!Isn't is faster to transpose the matrix and then sum over the columns?
! Richard Maine suggests not likely since implementation is compiler
! dependent.

  b = sum(transpose(a),dim=1)/n2
  print *, "b=",b

end program ArrayExample