Hi Jim, I forwarded your query to folks here at GFDL, and hope you do not mind my posting this information also on the mom4-list so that others in the mom4 community can read.
Ron Pacanowski responds below. Bottomline: we need the full 64 bit precision. Best, Steve Ron Pacanowski wrote: > > Hi Steve, > > 32 bit precision leads to signifcant roundoff in important places. One > might expect roundoff to be both positive and negative which would tend to > cancel over time. One example of where this is not the case is in the > thermocline. Due to the shape of the thermocline , roundoff is of only one > sign there and accumulates in one direction over time. So, 64 bits is of > precision is needed and is not a legacy issue. Before vector machines, the > basic word size was 32 bits and critical places in the code had to be made > double precision. Going back to this idea would be ill advised. > > Ron P. > > > -------- Original Message -------- > > Subject: MOM4 and ocean models > > Date: Tue, 22 Jul 2003 10:11:52 -0400 > > From: James Abeles <[EMAIL PROTECTED]> > > To: [EMAIL PROTECTED] > > > > Dr. Griffies, > > I work for IBM and support world-wide weather. I have a question about > > floating point precision in ocean models.In MOM you use 64 bit precision > > for reals. Is it really needed or is it just legacy from the days when > > vector computers only had 64 bit precision? If it is needed, could you > > explain why? > > > > Jim Abeles > > IBM Corporation: Deep Computing Technical Sales > > 301 879-3283 - work > > [EMAIL PROTECTED] -- Dr. Stephen M. Griffies phone: +1-609-452-6672 Geophysical Fluid Dynamics Laboratory FAX: +1-609-987-5063 P.O. Box 308, Forrestal Campus Site B email: [EMAIL PROTECTED] Princeton, NJ 08542 USA http://www.gfdl.noaa.gov/~smg ------------------------------------------------------- This SF.net email is sponsored by: VM Ware With VMware you can run multiple operating systems on a single machine. WITHOUT REBOOTING! Mix Linux / Windows / Novell virtual machines at the same time. Free trial click here: http://www.vmware.com/wl/offer/345/0 _______________________________________________ FMS-mom4 mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/fms-mom4
