Dear Steve, ----- Mensaje original ----- > De: "Gfortran List" org> > Para: "Jorge D'Elia" conicet.gov.ar> > CC: "Gfortran List" org> > Enviado: Viernes, 21 de Abril 2023 19:53:26 > Asunto: Re: coarrays using extended precision (80 bits) ? > > On Fri, Apr 21, 2023 at 08:33:31AM -0300, Jorge D'Elia wrote: >> Dear GFortran developers, >> >> One question: is there any chance of encoding with coarrays using >> extended precision (80 bits) at least inside a multicore computer? >> (as if to simplify a bit). >> >> To date, the possibility of using double precision (64 bits) or >> extended precision (80 bits) is an alternative in our production >> code, but sometimes we would like to do computations in >> 80 bits and, in certain parts, there are coarrays. >> We have validated even in quadruple precision (128 bits), using >> ifort although, as is well known, the CPU times are largely >> excessive. >> >> Thanks in any case. >> > > Well, I just installed OpenCoarray and downloaded a pi/4 > monte carlo code that Thomas wrote using REAL. I changed > everything to use REAL(10). Compiled and executed without > a problem. I also tested REAL(16), which worked although > it's painfully slow due to software floating point. So, > I guess I don't understand what you're asking? > > -- > Steve
Thanks a lot for your answer. Now: Since we were noticing numerical issues in certain cases in our code, we moved on to a toy model. The toy model is based on a standard LU factorization with a dense block-distributed system matrix. So: 1/2) When we use gfortran+opencoarrays: The verification computation of the numerical solution of the system of equations is OK if we use precision either (single, double, extended, quadruple) when the number Z of images is equal to 1. It is also OK if we use precision either (single, double) when Z>1. But it fails if we use precision either (extended, quadruple) when Z>1. 2/2) When we use ifort: The verification computation of the numerical solution of the system of equations is OK if we use precision either (single, double, quadruple) either when Z=1 or when Z>1. We cannot check it in extended precision because ifort does not support the use of extended precision. As a first attempt to explain the discrepancy, we assume that those verification failures in the solution could be attributed to gfortran+opencoarrays not quite correctly transmitting numbers in extended precision, because opencoarrays relies on some standard MPI for single and double precision (it would be like this?). Best regards. Jorge. -- CIMEC (UNL-CONICET), cimec.conicet.gov.ar, www.cimec.org.ar
