CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

OpenFOAM Double precision vs Single Precision

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   June 11, 2008, 09:11
Default Hi Foamers I am trying to s
  #1
Senior Member
 
Alexandre Pereira
Join Date: Mar 2009
Posts: 155
Rep Power: 8
alexandrepereira is on a distinguished road
Hi Foamers

I am trying to solve a BIG CFD problem in a NOT SO BIG computer, so i had this idea, correct me if i am wrong here:

Using the precompiled OpenFOAM single precision or compile it and use it in my problem should roughly be the same as "doubling" the memory capacity, since the float representation requirements in C++ is roughly half the double float representation requirements;

So that shoul be enough to solve a problem with a size double of the ones that i solve in double precision, but there is a catch ( at least i think so )... :

Due to the reduced precision, the effect of round up errors may simply abort convergence of the solvers in OpenFOAM... or increase drastically the number of iterations needed for convergence...

Does anybody has experience in this...?

Best Regards

Alex
alexandrepereira is offline   Reply With Quote

Old   June 11, 2008, 14:30
Default It's quite possible. CG solver
  #2
Senior Member
 
Sandeep Menon
Join Date: Mar 2009
Location: Amherst, MA
Posts: 386
Rep Power: 15
deepsterblue will become famous soon enough
It's quite possible. CG solvers, for instance, update search directions based on the residual dot-product of the previous iteration. If the dot-product is inaccurate due to round-off, the search direction falters a little bit, and hence the convergence issues.
__________________
Sandeep Menon
University of Massachusetts Amherst
https://github.com/smenon
deepsterblue is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
single - double precision PC FLOW-3D 4 October 16, 2008 19:28
Single or double precision Jonas Larsson Main CFD Forum 15 March 26, 2007 23:15
CFX 64bit single-double precision Tom CFX 2 December 19, 2006 16:39
Compiling OpenFOAM 12 in Single Precision fra76 OpenFOAM Installation 5 April 21, 2006 12:05
Single v.s. double precision Confused CFX 9 April 19, 2004 18:33


All times are GMT -4. The time now is 11:50.