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False error reports for correct program

 
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mecej4



Joined: 31 Oct 2006
Posts: 1693
PostPosted: Sun May 01, 2022 1:19 pm    Post subject: False error reports for correct program Reply with quote
The following program is quite simple and it should be possible to compile and run this program with no errors.

Code:
program pgm
   implicit none
   real, dimension(:,:), allocatable :: ev
   integer i, nsub, mi

   nsub = 10
   mi = 5
   ev = reshape( gaussian(nsub*mi),(/mi,nsub/) )
   print *,(ev(1,i),i=1,5)

   contains

   function gaussian(n)
! return an array of gaussian random variates with variance 1
   integer :: n
   real, dimension(n) :: gaussian
   real, dimension(n) :: rn
   real :: rn1,rn2,arg,x1,x2,x3
   real, parameter :: pi=4.0d0*atan(1.0)
   integer :: i
   if(mod(n,2) /= 0)stop 'Gaussian: argument must be an even integer'
   call random_number(rn)
   do i=1,n/2
      rn1=rn(2*i-1)
      rn2=rn(2*i)
      arg=2.0*pi*rn1
      x1=sin(arg)
      x2=cos(arg)
      x3=sqrt(-2.0*log(rn2))
      gaussian(2*i-1)=x1*x3
      gaussian(2*i)=x2*x3
   enddo
   end function gaussian

end program


With no options or with /debug, the program aborts with

Code:
     Error: Nonconformant arrays


With /64 /check, the program aborts with

Code:
     Integer arithmetic overflow
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PaulLaidler
Site Admin


Joined: 21 Feb 2005
Posts: 7297
Location: Salford, UK
PostPosted: Mon May 02, 2022 9:40 am    Post subject: Reply with quote
mecej4

Thank you for the feedback on this false error report. This is another instance of "allocate on assignment" not working. At the moment an explicit allocate

Code:
allocate(ev(mi,nsub))


is required before the call to RESHAPE.

It is interesting that you class this as a "simple" program. My first impression is that a fix will be quite difficult.
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mecej4



Joined: 31 Oct 2006
Posts: 1693
PostPosted: Mon May 02, 2022 9:53 am    Post subject: Reply with quote
Quote:
It is interesting that you class this as a "simple" program.


Sorry, I guessed that because the allocation size of the array is knowable at compile time the compiler's job could be "simple".
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JohnCampbell



Joined: 16 Feb 2006
Posts: 2387
Location: Sydney
PostPosted: Mon May 02, 2022 9:54 am    Post subject: Reply with quote
Does function gaussian require a RESULT statement for where the value of the function is an array?

I thought this was a requirement for Fortran 95 ?
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mecej4



Joined: 31 Oct 2006
Posts: 1693
PostPosted: Mon May 02, 2022 11:01 am    Post subject: Reply with quote
Indeed, Fortran 95 requires:

Quote:
If the function result is array valued or a pointer, this shall be specified by specifications of the name of the result variable within the function body


Later version of Fortran allow a declaration type spec to be used as a prefix spec in the FUNCTION statement as an alternative to a RESULTS clause.

We are grateful that FTN95 supports many of these features, although they did not exist in Fortran 95.
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