[gmx-users] setting up mpi code

[Cesar Araujo]

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