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Array argument for a statement function

 
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Kenneth_Smith



Joined: 18 May 2012
Posts: 703
Location: Hamilton, Lanarkshire, Scotland.

PostPosted: Wed Sep 20, 2023 12:11 pm    Post subject: Array argument for a statement function Reply with quote

I am trying very hard to break the habit of using nested do loops for everything, i.e. use array operations where possible.

In the following code, I think I am breaking the rules of Fortran, but FTN95 does not report any ERROR or WARNING.

What I see here is FTN95 accepting an array argument for a one line statement function, which I think is not allowed?

Is my understanding correct (a bug) or am I missing something in my understanding?

Code:
program p2
implicit none
integer, parameter :: n = 4
real*8 :: x(n) = 0, y(n) = 0, z(n,n) = 0
integer i,j
real*8  f, a, b
!Statement function to define a function f of two scalars x and y.
   f(a,b) = a + b
 
   x = [1,2,3,4]
   y = [1,2,3,4]

   do i = 1, n
     z(:,i) = f(x(:), y(i))    ! Should FTN95 not generate a fatal ERROR here?
   end do

   print*, 'Using array operation to eliminate one do loop and a statement function'
   do i = 1, n
     print*, (z(i,j),j = 1,n)
   end do
   print*

!  This is allowed because f2 is elemental
   do i = 1, n
     z(:,i) = f2(x(:), y(i))
   end do

   print*, 'Using array operation to eliminate one do loop using elemental function'
   do i = 1, n
     print*, (z(i,j),j = 1,n)
   end do

   contains

   real*8 elemental function f2(c,d)
   real*8, intent(in) :: c, d
     f2 = c+d
   end function f2
   
end program p2


i.e. Is the assigment:
Code:
z(:,i) = f(x(:), y(i))

valid fortran in this context?
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