From: tkoenig@netcologne.de   
      
   pehache  schrieb:   
   > Le 16/11/2023 à 02:28, gah4 a écrit :   
   >> On 11/4/23 2:21 PM, Steven G. Kargl wrote:   
   >>> The SCALE intrinsic allows one to change the   
   >>> floating point exponent for a REAL entity.   
   >>> For example,   
   >>>   
   >>> program foo   
   >>>     real x   
   >>>     x = 1   
   >>>     print *, scale(x,1) ! print 2   
   >>> end program   
   >>>   
   >>> This scaling does not incur a floating point   
   >>> rounding error.   
   >>>   
   >>> Question.  Anyone know why the Fortran standard (aka J3)   
   >>> restricted X to be a REAL entity?  It would seem that X   
   >>> could be COMPLEX with obvious equivalence of   
   >>>   
   >>> SCALE(X,N) = COMPLX(SCALE(X%RE,N),SCALE(X%IM,N),KIND(X%IM))   
   >>>   
   >>> Should the Fortran be amended?   
   >>   
   >>   
   >> Wow, no answer yet.   
   >>   
   >> It does seem that sometimes Fortran is slow to add features, especially   
   >> when need for them isn't shown.   
   >   
   > The reason is maybe because the standard doesn't specify how a complex   
   > number is internally represented.   
      
   I disagree almost entirely.   
      
   Subclause 19.6.5 of F2018, "Events that cause variables to become   
   defined" has   
      
   (13) When a default complex entity becomes defined, all partially   
   associated default real entities become defined.   
      
   (14) When both parts of a default complex entity become defined as   
   a result of partially associated default real or default complex   
   entities becoming defined, the default complex entity becomes   
   defined.   
      
   Which means that something like   
      
     real :: a(2)   
     complex :: c   
     equivalence (a,c)   
      
   allows you to set values for a(1) and a(2) and you can expect the   
   components of c to get the corresponding values.   
      
   This is important for FFT.   
      
   Now, you might argue that the compiler can invoke "as if", but there   
   is no practical way to use any other complex representation.   
      
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