* Unexpected NaN value
@ 2018-10-04 20:26 Luca Donatini
2018-10-04 20:30 ` Thomas Koenig
0 siblings, 1 reply; 3+ messages in thread
From: Luca Donatini @ 2018-10-04 20:26 UTC (permalink / raw)
To: fortran
Dear all,
I noticed a strange behaviour of the gfortran compiler.
In the source file below, when the real variable b has an "integer-like"
value (e.g. "2", "2.", "2.0" ...) the code correctly writes out a numerical
result. But when a "real-like" value is assigned to b (e.g. "2.1",
"2.0000009", "2.83" ...) , the code writes a NaN value.
This does not occurr when the sample code is compiled with an Intel
compiler (I tested version 2018a).
I have the NaN value problem with both:
- gfortran 8.2.1 20180831 (Arch Linux package)
- gfortran 6.3.0 20170516 (Debian Stretch package).
Is this a bug? A known one?
Many thanks in advance for all the clarifications,
Luca Donatini
*** example source file ***
program test
implicit none
real :: a = -1.57079637
real :: b = 2.1
write(*,*) cos(a)
write(*,*) cos(a) **(2*b)
end program
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: Unexpected NaN value
2018-10-04 20:26 Unexpected NaN value Luca Donatini
@ 2018-10-04 20:30 ` Thomas Koenig
2018-10-04 21:17 ` Luca Donatini
0 siblings, 1 reply; 3+ messages in thread
From: Thomas Koenig @ 2018-10-04 20:30 UTC (permalink / raw)
To: Luca Donatini, fortran
Hi Luca,
> program test
> implicit none
>
> real :: a = -1.57079637
> real :: b = 2.1
>
> write(*,*) cos(a)
> write(*,*) cos(a) **(2*b)
>
> end program
cos(a) happens to be negative, so cos(a)**(2*b) is undefined,
because 2*b is real. And yes, this is expected.
Regards
Thomas
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Unexpected NaN value
2018-10-04 20:30 ` Thomas Koenig
@ 2018-10-04 21:17 ` Luca Donatini
0 siblings, 0 replies; 3+ messages in thread
From: Luca Donatini @ 2018-10-04 21:17 UTC (permalink / raw)
To: Thomas Koenig; +Cc: fortran
Dear Thomas,
Many thanks for the clarification!
Best regards,
Luca
Il gio 4 ott 2018, 22:30 Thomas Koenig <tkoenig@netcologne.de> ha scritto:
> Hi Luca,
>
> > program test
> > implicit none
> >
> > real :: a = -1.57079637
> > real :: b = 2.1
> >
> > write(*,*) cos(a)
> > write(*,*) cos(a) **(2*b)
> >
> > end program
>
> cos(a) happens to be negative, so cos(a)**(2*b) is undefined,
> because 2*b is real. And yes, this is expected.
>
> Regards
>
> Thomas
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2018-10-04 21:17 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-10-04 20:26 Unexpected NaN value Luca Donatini
2018-10-04 20:30 ` Thomas Koenig
2018-10-04 21:17 ` Luca Donatini
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).