[gmx-users] setting up mpi code

[Erik Lindahl]

Hi,

Right - but essentially all of the comparison icc warns about in  
Gromacs are cases where the number has previously been set to exact  
zero (=function disabled), and the check is just to see whether the  
option is enabled or not. The number won't magically change to non- 
zero in the meantime, so for this type of comparisons it's completely  
correct.

Cheers,

Erik


On Nov 9, 2005, at 10:58 PM, Cesar Araujo wrote:

>
> Hi,
>
> Floating-point comparisons are not exact due to the limited precision
> representation and in most cases they suffer from round-off errors.  
> This is not
> the best way to compare a floating-point variable value against  
> zero value or
> even between them. Please, check the book "Numerical Recipes in C"  
> for further
> details about this topic. Here you will find a good practical  
> explanation:
>
> http://www.cygnus-software.com/papers/comparingfloats/ 
> comparingfloats.htm
>
> If the things doesn't work as expected this could be a probable cause.
>
> Regards,
> César.-
>
> ----------------------------------
> Hi
>
> I have been trying to get gromacs 3.2.1 set up with mpi on our sgi  
> cluster at
> work. I get a number of errors that i have not received when i have  
> compiled
> previously on serial intel nodes, e.g:
>
> orires.c(95): warning #1572: floating-point equality and inequality  
> comparisons
> are unreliable
>     if (ir->orires_tau == 0)
>                        ^
>
> orires.c(104): warning #1572: floating-point equality and  
> inequality comparisons
> are unreliable
>     if (ir->orires_tau == 0)
>                        ^
>
> orires.c(209): warning #1572: floating-point equality and  
> inequality comparisons
> are unreliable
>               (eig[j] != 0) ? eig[i]/eig[j] : 0,v[XX][i],v[YY][i],v 
> [ZZ][i]);
>                       ^
>
> orires.c(230): warning #1572: floating-point equality and  
> inequality comparisons
> are unreliable
>     bTAV = (od->edt != 0);
>                     ^
>
> orires.c(415): warning #1572: floating-point equality and  
> inequality comparisons
> are unreliable
>     if (od->fc != 0) {
>                ^
>
> orires.c(416): warning #1572: floating-point equality and  
> inequality comparisons
> are unreliable
>       bTAV = (od->edt != 0);
>                       ^
>
> plus lots lots more along the same lines!
>
> But the code does not fail and seems to compile completely, i.e.  
> luck works!
>
> Should I be concerned about these errors?
>
> I am using icc, ifort and lmpi
>
> Thanks
> Jo
>
>
>
> -- 
> Cesar Araujo, Lic. of Chemistry
> Department of Molecular Endocrynology
> Oulu University Hospital
> FIN-90029 OYS, FINLAND
>
> phone: +358 8 3155632
> e-mail: cesar.araujo at oulu.fi
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-----------------------------------------------------------
Erik Lindahl  <lindahl at sbc.su.se>
Assistant Professor, Stockholm Bioinformatics Center
Stockholm University, SE 106 91 Stockholm
Phone: +46 8 5537 8564     Fax: +46 8 5537 8214