 |
 |
> Date: Mon, 2 Oct 2000 10:30:31 -0700 > From: Ian Chivers <[log in to unmask]> > On Mon, 02 Oct 2000 19:55:34 +0010 [log in to unmask] > wrote: > > > Juergen VonHagen wrote (little bits snipped for brevity):: > > > > >robin wrote: > > >> > > >> > From: Aleksandar Donev <[log in to unmask]> > > >> > > >> > I have a pedagological question for the Fortran teachers out there. > > > > Variants of this are not only useful for teachers, but also practitioners. > > > > >> > How does one write "best" an expression with mixed types, say: > > >> > > > >> > complex(kind=sp) :: x,y > > >> > integer :: k > > >> > > > >> > y=(k-1)/(k+1)*x > > > > If k is positive, the first part (integer arithmetic) is always 0, so y is 0 > > If k is zero, y = -x > > If k is negative (except -1), y = 2.*x > > > > This assumes left to right evaluation, so (k+1)/(k-1) is integer arithmetic. I > > believe this is part of the standard, but would bow to RM's better knowledge. > > If it is not, I have screwed up big time over many years, but my vendors seem to > > believe what I do. > > i don't have a copy of the standard at hand so can't quote the exact > wording. fortran 90 allowed expressions to be replaced with > a mathematically equivalent one. as this expression involves > integer arithmetic i would have thought that (k-1)/(k+1) > has to be done first. Doing (k-1)/(k+1) first will produce a zero result (k > 0). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%