gfortran compiler precision

[Tim Prince]

miguel jiménez Zapata wrote:
> Hi,
> 
> I'm a newcomer to programming!
> I'm using two compilers to compile exactly the same
> fortran 90 program. I'm using gfortran and visual
> fortran
> (shame on me!). The thing is that the numeric results
> I get with these two different compilers start
> differing from the 7th decimal digit. Could anybody
> explain me why does this happen? I use double
> precision numbers.
> 
To complete your checking whether the difference is due to single 
precision slipping in somewhere, you should of course use IMPLICIT NONE 
to make sure you have no default real variables, and check that you have 
no default real constants, other than those which are exact in single 
precision.  CVF has an option to promote constants to double in context; 
it may have been on by default in early versions, or it may be set by 
other options such as /fpscomp.